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Title:
RAINWATER HARVESTING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2010/142950
Kind Code:
A1
Abstract:
A water storage system is disclosed comprising a tank (30), a sensor (38) for determining the level of water in the tank (30), an outlet (40) for allowing water to exit the tank (30), and a valve (42) for controlling the flow of water through the outlet (40). The system is configured to vary the manner in which the valve (42) is opened depending on the level of water determined to be inside the tank (30).

Inventors:
GEORGE, David (Arup, 63 St Thomas Street, Bristol BS 1 6JZ, GB)
Application Number:
GB2010/001128
Publication Date:
December 16, 2010
Filing Date:
June 07, 2010
Export Citation:
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Assignee:
OVE ARUP & PARTNERS INTERNATIONAL LTD (13 Fitzroy Street, London W1 T 4BQ, GB)
GEORGE, David (Arup, 63 St Thomas Street, Bristol BS 1 6JZ, GB)
International Classes:
E03B3/03; E03D5/00; G05D7/06
Domestic Patent References:
2007-07-26
2008-04-03
Foreign References:
GB2325253A1998-11-18
DE20014664U12000-12-07
DE3536691A11987-04-16
GB0907705A2009-05-05
Attorney, Agent or Firm:
CHIVA, Andrew Peter (Dehns, St. Bride's House10 Salisbury Square, London EC4Y 8JD, GB)
Download PDF:
Claims:
10256301cl

Claims :

1. A water storage system comprising a tank, a sensor for determining the level of water in the tank, an outlet for allowing water to exit the tank, and a valve for controlling the flow of water through the outlet, wherein the system is configured to vary the manner in which the valve is opened depending on the level of water determined to be inside the tank.

2. A water storage system as claimed in claim 1, wherein the system is configured to open the valve in a manner whereby the size of the valve conduit that the water flows through is selected depending on the level of water determined to be inside the tank.

3. A water storage system as claimed in claim 2, wherein the system controls the valve so as to provide a large conduit when the level of water is determined to be low and a small conduit when the level of the water is determined to be high.

4. A water storage system as claimed in claim 2 or 3, wherein the valve is controlled such that the lower the level of water is determined to be, the greater the amount by which the valve conduit is opened.

5. A water storage system as claimed in any preceding claim, wherein the valve is biased closed and is opened automatically at a pre-programmed time or is opened after being activated by a user.

6. A water storage system as claimed in any preceding claim, wherein the valve is automatically closed after a predetermined period of time after having been opened.

7. A water storage system as claimed in any one of claims 1-5, wherein the valve is biased closed and the system is configured to select the length of time that the valve opens depending on the level of water determined to be inside the tank.

8. A water storage system as claimed in claim 7, wherein the system controls the valve such that when the level of water in the tank is detected as being low the valve is opened for a long time and when the level of water in the tank is detected as being high the valve is opened for a short time.

9. A water storage system as claimed in claim 7 or 8, wherein the valve is controlled such that the higher the level of water determined to be in the tank, the shorter the period of time that the valve is opened for.

10. A water storage system as claimed in any preceding claim, wherein the valve is provided inside of the tank.

11. A water storage system as claimed in any one of claims 1-9, wherein the valve is provided in a water pipe located outside of the tank and in fluid communication with the outlet.

12. A water storage system as claimed in any preceding claim, wherein the sensor for determining the level of water in the tank comprises at least one of; a radar sensor for detecting the position of the water surface; a float sensor; a pressure sensor; and an electrical conductivity sensor.

13. A system comprising a rainwater catchment area, a sanitary fitting having a waste bowl, and a water storage system as claimed in any preceding claim, wherein said valve is a flush valve for allowing water to exit the tank and flush the waste bowl, wherein the system is configured such that rainwater flows directly from the catchment area into the tank, and wherein water flows directly from the tank into the waste bowl of the sanitary fitting when the flush valve is activated.

14. A system as claimed in claim 13, wherein the system is configured such that rainwater does not enter a water storage vessel as it flows from the rainwater catchment area to the tank, and wherein the water from the tank does not enter a water storage vessel as it flows from the tank to the waste bowl.

15. A system as claimed in claim 13 or 14, wherein the sanitary fitting is a toilet or urinal.

16. A system as claimed in claim 13, 14 or 15, wherein the rainwater catchment area is located higher than the tank so that the rainwater fills the tank under the effect of gravity alone.

17. A system as claimed in any one of claims 13-16, wherein the rainwater catchment area is a roof of a building and the sanitary fitting is located inside of the building.

18. A system as claimed in any one of claims 13-17, wherein the system is configured such that the rainwater passes through a filter before passing into the tank, and/or such that the rainwater passes through a filter arranged in the tank.

19. A system as claimed in any of claims 13-18, wherein the rainwater catchment area supplies rainwater directly to two or more tanks, each tank being associated with a flush valve for allowing water to exit the tank when activated, each tank supplying water directly to a waste bowl of a sanitary fitting when its respective valve is activated.

20. A system as claimed in any of claims 13-19, further comprising a second sanitary fitting having a waste bowl, a second water tank and a second flush valve for allowing water to exit the second tank and flush said second waste bowl, wherein said system is configured such that water is supplied directly from said rainwater catchment area into said second tank, and wherein water is supplied directly from said second tank into the second waste bowl when the second flush valve is activated.

21. A system as claimed in any of claims 13-20, comprising a plurality of waste bowls connected to each of the first and/or second tank, and wherein water is supplied directly from said first and/or second tank into said plurality of waste bowls when a respective flush valve is activated.

22. A system as claimed in any preceding claim, wherein the tank comprises an overflow outlet for allowing water to drain out of the tank when the tank has been filled with water to a first predetermined level.

23. A system as claimed in any preceding claim, wherein the system comprises a sensor for determining the level of water in the tank.

24. A system as claimed in claim 23, wherein the system is arranged and configured to determine when the level of water in the tank is below a second predetermined level .

25. A system as claimed in claim 24, wherein the tank is connected to a continual supply of water and the system is configured to selectively admit water from said supply when the water in the tank is determined to be below the second predetermined level .

26. A system as claimed in claim 24 or 25, wherein the system is arranged and configured to determine when the level of water in the tank is at or above a third predetermined level that is higher than the second predetermined level .

27. A system as claimed in claim 24, 25 or 26, wherein the system is configured to stop the admission of water into the tank from the continual supply when the water in the tank is at or above either the second or third predetermined level .

28. A method of supplying water to the waste bowl of a sanitary fitting comprising: collecting rainwater over a rainwater catchment area, directing the rainwater such that it flows directly from the catchment area into a tank, and allowing water to flow directly from the tank into the waste bowl of the sanitary fitting when a flush valve for allowing water to exit the tank is activated.

29. A system comprising a sanitary fitting having a waste bowl, a water tank and a flush valve for allowing water to exit the tank and flush the waste bowl, and a source of reclaimed water arranged above the tank, wherein the system is configured such that reclaimed water flows directly from the source into the tank, and wherein water flows directly from the tank into the waste bowl of the sanitary fitting when the flush valve is activated.

Description:
Rainwater Harvesting System

The present invention relates to a rainwater harvesting system and in particular to a system for supplying water to a sanitary fitting such as a toilet or urinal .

It is well known to collect water from the rooftops or other surfaces of buildings. Traditionally rainwater falling on a roof is diverted into a system of gutters and drainpipes which carry the rainwater into the sewers . It is usually desired to remove water from the roof as quickly as possible to reduce the chances of water leaking into the building. More recently, due to environmental and economic considerations, rainwater has been collected and used, rather than being directed straight into the sewers. The collected rainwater can be used for outdoor purposes such as the irrigation of gardens or can be used domestically within buildings for non-drinking purposes. Use of rainwater in this way, reduces the amount of (potable) mains water required. This has economic and environmental benefits .

Traditionally, rainwater collected for use within a building is stored in a tank somewhere nearby the building. Due to the considerable weight of the laden tank, the tank is located in a basement or cellar. The water from this tank is then pumped to, for example, the toilet cistern to enable it to be flushed. The tank, associated piping and pumps may be rather bulky, inconvenient and expensive to install within a building.

It is therefore desired to provide an improved system for supplying rainwater to a sanitary fitting. The present invention provides a system comprising a rainwater catchment area, a sanitary fitting having a waste bowl, a water tank and a flush valve for allowing ■ water, to exit the tank and flush the waste bowl, wherein the system is configured such that rainwater flows directly from the catchment area into the tank, and wherein water flows directly from the tank into the waste bowl of the sanitary fitting when the flush valve is activated. Λ For the avoidance of doubt, the term 'rainwater flows directly from the catchment area into the tank' is intended to mean that water is not stored between the catchment area and the tank. Rather, the catchment area is in direct fluid communication with the tank so that rainwater can flow continually from the catchment area directly into the tank. The rainwater may however pass through non-storage components of the system arranged between the catchment area and the tank. For example, the rainwater may be filtered between the catchment area and the tank. Similarly, the term 'water flows directly from the tank into the waste bowl ' is intended to mean that water is not stored between the tank and the waste bowl. The water may flow continually from the tank directly into the waste bowl when the valve is activated. The present invention effectively directs rainwater directly into a tank acting as the flushing cistern of a sanitary fitting, such as a toilet or urinal. There is therefore no need to provide a large rainwater storage tank, as is conventional. Typically, these storage tanks are so large and heavy that they are required to be stored outside of the building in which the sanitary fitting is located, thus requiring rainwater to be pumped to the toilet cistern for use in flushing the toilet. The present invention avoids the need for such a tank and also the need to pump rainwater to the sanitary fitting in order to flush it. In the preferred embodiment, the tank is located in the conventional position for a cistern, i.e. above and preferably within a five meters of the waste bowl.

The rainwater catchment area is an area over which rainwater falls and is collected. According to the preferred embodiments, the rainwater catchment area is located higher than the tank so that the rainwater fills the tank under the effect of gravity alone. Preferably, the rainwater catchment area is a roof of a building and the sanitary fitting is preferably located inside of the building. In this embodiment, the rainwater is preferably collected by the roof and directed to a roof drainage outlet. The roof drainage outlet is in direct fluid communication with the tank such that rainwater flows directly from the roof into the tank without being stored therebetween. The roof drainage outlet and tank are connected by a down pipe. It will be understood that other surfaces may be used as the rainwater catchment area, such as walls or gutters of buildings.

In the preferred embodiments the rainwater passes through a filter to remove debris before passing into the tank. A preferred filter is disclosed in GB 0907705.8, although other filters may be used. Additionally, or alternatively, a filter may be provided inside of the tank to filter the rainwater.

The tank preferably comprises an overflow outlet for allowing water to drain out of the tank when the tank has been filled to a first predetermined level. The overflow outlet is preferably connected to the building drainage or sewerage system so as to prevent the tank from overflowing and flooding part of the building. Preferably, the overflow outlet is arranged towards the top of the tank.

The system preferably comprises a sensor for determining the level of water in the tank. Preferably, the system is arranged and configured to determine when the level of water in the tank is below a second predetermined level . The tank is preferably connected to a continual supply of water and the system is configured to selectively admit water from said supply when the water in the tank is determined to be below the second predetermined level. It will be appreciated that the second predetermined level is lower than the first predetermined level at which the overflow outlet is located. Preferably, the system is configured to stop or reduce the rate of admission of water from the continual supply when the water in the tank is at or above the second predetermined level. Alternatively, the system may be arranged and configured to determine when the level of water in the tank is at or above a third predetermined level that is higher than the second predetermined level. In this embodiment, the system is configured to stop or reduce the rate of admission of water from the continual supply when the water in the tank is at or above the third predetermined level. It will be appreciated that the third predetermined level is also lower than the first predetermined level at which the overflow outlet is located.

The system preferably comprises a valve in the continual supply of water, the valve being controlled based on the level of water determined by the sensor. Preferably, the valve is an electronically activated valve, such as a solenoid valve. However, any other type of valve may be provided as long as it can be controlled to selectively admit water as described above. For example, the valve may be a mechanical valve actuated by a sensor such as a ballcock floating on the water. The inlet in the tank for the water from the continual supply is preferably located at the top of the tank. The inlet is preferably located to remain above the level of water in the tank at all times. Most preferably, the inlet is at a level above the level of the overflow outlet. Preferably, the continual supply of water is the mains water supply. The sensor for determining the level of water may take any form. In a particularly preferred embodiment the sensor is located so as to remain above the water level at all times (i.e. preferably above the overflow outlet) and is configured to transmit a signal towards the water and receive a signal reflected from the water. The sensor may have a single component for both transmitting and receiving the signals or may have separate components to fulfil these functions. The sensor preferably determines the time elapsed between transmitting the signal and receiving the reflected signal, and uses this time to calculate the distance of the surface of the water from the sensor. This distance indicates the level of water in the tank. Therefore, the sensor is preferably a radar sensor. The sensor may transmit and receive any type of signal that is suitable for being reflected from water and then detected. This includes electromagnetic waves such as, for example, infra-red light but also other types of signals such as sonic and ultra-sonic waves. In another embodiment one of the transmitter and receiver may be located above the water and the other of the transmitter and receiver is configured to float at or near the surface of the water. In this embodiment the level of the water is determined from the time it takes a signal to pass from the transmitter to the receiver. In this embodiment the signal is not reflected off the surface of the water.

In another embodiment the sensor comprises a float mechanism that floats at or near the surface of the water and which is mechanically connected to the valve of the continual water supply such that the change in height of the float within the tank controls the opening and closing of the valve in the continual water supply. For example, the sensor may be a conventional ballcock mechanism.

In another embodiment the sensor comprises electrodes which become electrically connected by the presence of water between them so as to indicate the level of water in the tank. A pair of electrodes may be located on a wall of the tank at the second predetermined level, i.e. at the minimum level of water desired to be maintained in the tank. When an electrical connection is not made between the electrodes the level of water is determined to be below the second predetermined level.

Similarly, a pair of electrodes may also be located on a wall of the tank at the third predetermined level such that when an electrical connection is made between these electrodes the level of water is determined to be at or above the third predetermined level .

In yet another embodiment the sensor comprises a pressure sensor which determines the level of water in the tank from the pressure exerted on the sensor. In this embodiment, the sensor is preferably located at or near the bottom of the tank.

It will be appreciated that types of sensors other than those mentioned above may be used and that a combination of two or more of the same or different types of sensors could be used in the invention. The sensor may be selected so as to be able to detect any level of water in the tank. Alternatively, the sensor is less preferably configured to detect only the second predetermined level, or only the second and third predetermined levels.

Preferably, the system uses the sensor to determine and monitor the volume of water that has entered the tank from the rainwater catchment area and/or from the continual supply of water over a given period of time. The system may be configured to monitor the volume of water that enters the tank from the continual water supply by monitoring the length of time the valve in the continual water supply is open for and from the knowledge of the inflow rate of water through this valve. It is particularly preferable that the system comprises a sensor for determining the level of water in the tank, and that the system controls the length of time that the flush valve is opened for after it has been activated in dependence on the level of water determined to be in the tank.

Preferably, the system controls the flush valve such that if the level of water in the tank is detected as being relatively low when the flush valve is activated, the flush valve is opened for a relatively long time before it is closed again. The flush valve is also controlled such that if the level of water in the tank is detected as being relatively high when the flush valve is activated, the flush valve is opened for a relatively short time before it is closed again. The flush valve is preferably controlled such that the higher the level of water is determined to be in the tank the shorter the period of time that the flush valve is opened for before being closed again. The higher the level of water in the tank the higher the pressure at the flush valve. As a consequence the flow rate of water through the flush valve increases the more water that there is in the tank. By controlling the period of time that the flush valve is opened for depending on the level of water that is in the tank the preferred embodiment ensures that a reasonably constant volume of water is used for flushing the waste bowl, irrespective of the amount of water in the tank. This has been recognised as being particularly important in a rainwater filled tank, wherein the level of water can vary significantly depending on the amount of rainfall and because such tanks tend to have a large total water storage capacity. In a preferred embodiment the tank has a water storage capacity selected from one of: at least 2OL; at least 5OL; at least 10OL; at least 150L; or at least 200L. In some embodiments, the tank may have a storage capacity of a conventional toilet or urinal cistern.

In addition, or as an alternative, to controlling the period of time that the flush valve is opened for the amount by which the flush valve is opened may be controlled depending on the level of water in the tank. Preferably, the system controls the flush valve such that if the level of water in the tank is detected as being relatively low when the flush is activated, the flush valve is opened by a relatively large amount before it is closed again. The flush valve is also controlled such that if the level of water in the tank is detected as being relatively high when the flush valve is activated, the flush valve is opened by a relatively small amount before it is closed again. The flush valve is preferably controlled such that the lower the level of water in the tank is determined to be, the greater the amount by which the flush valve is opened before being closed again. The size of the conduit through the flush valve may therefore be altered so as to provide a constant volume of water each time the flush valve is activated, even when the water is at different levels in the tank.

As described above, the duration of time for which the flush valve is opened and/or the amount by which it is opened after it has been activated is preferably controlled depending on the level of water detected to be in the tank. The level of water may be determined for the purpose of controlling the valve at the time the flush valve is activated. Alternatively, or additionally, an embodiment of the system is configured to determine the level of water in the tank periodically and store it. In this embodiment the level of water which has been stored most recently at the time the flush valve is activated may be used to control the duration of opening and/or the amount of opening of the flush valve. The system is preferably configured to activate the flush valve after an. input from the user. The system may include a mechanical flushing handle for the user to activate the flush valve and/or an electronic sensor for the user to activate the flush valve. The embodiments of the invention are also preferably configured to provide a partial flush (e.g. a half flush) or a full flush, depending on an input from the user. Additionally, or alternatively, the system may be configured to automatically open the flush valve after having detected the presence of a user in the vicinity of the waste bowl and/or to automatically activate the flush valve at predetermined time intervals. Although the rainwater catchment area has been described above as supplying rainwater directly to only a single tank associated with a sanitary fitting, the rainwater catchment area may supply rainwater directly to two or more tanks, each of which supplies water directly to a waste bowl of a sanitary fitting. Embodiments are contemplated wherein the rainwater catchment area supplies rainwater directly to three, four, five or even more tanks, each of which supplies water directly to a waste bowl of a sanitary fitting. Where the rainwater catchment area is a roof, a plurality of the tanks may be connected to the same roof outlet or to different roof outlets. This provides a decentralised system which avoids the need for a large, heavy rainwater tank and its associated pumps. Also, this enables the diameter of each down pipe to be relatively small, making installation of the system easier.

It is also contemplated that water may be supplied directly from a tank to two or more different waste bowls. For example, the tank may act as a communal cistern for two or more toilets or urinals. In these embodiments, the tank may have a separate flush valve associated with each waste bowl that it supplies with water. However, in other embodiments the tank has a single flush valve associated with all of the waste bowls that the tank supplies with water. This is useful, for example, where the tank automatically supplies water to a plurality of urinals to automatically flush them out at predetermined time intervals . The tank preferably has at least one removable access panel through which access into the tank can be gained. Preferably, at least one wall of the tank comprises a window for viewing into the tank. The window may be removable to act as an access panel The present invention also provides a method of flushing the waste bowl of a sanitary fitting comprising: collecting rainwater over a rainwater catchment area, directing the rainwater such that it flows directly from the catchment area into a tank, and allowing water to flow directly from the tank into the waste bowl of the sanitary fitting when a flush valve for allowing water to exit the tank is activated.

It has also been recognised that the above principles of the invention can be applied to sources of reclaimed water other than a rainwater catchment area. It is contemplated that the rainwater catchment area mentioned above may be replaced by a different source of reclaimed water that is located above the tank. For example, the system may comprise a swimming pool filter located above the tank, e.g. the pool may be on the roof of the building. The filtered water reclaimed by the pool filter is then channelled into the tank in the same manner as the rainwater is in the above-described embodiments. Alternatively, the source of reclaimed water may be a cooling tower for extracting water from hot fluids and gases. The extracted water is then channelled into the tank in the same manner as the rainwater is in the above-described embodiments .

Embodiments are contemplated corresponding to the embodiments described above except wherein the rainwater that is channelled to the tank is replaced by reclaimed water from the pool filter or cooling tower.

Accordingly, the present invention provides a system comprising a sanitary fitting having a waste bowl, a water tank and a flush valve for allowing water to exit the tank and flush the waste bowl, and a source of reclaimed water arranged above the tank, wherein the system is configured such that reclaimed water flows directly from the source into the tank, and wherein water flows directly from the tank into the waste bowl of the sanitary fitting when the flush valve is activated.

The present invention also provides a water storage system comprising a tank, a sensor for determining the level of water in the tank, an outlet for allowing water to exit the tank, and a valve for controlling the flow of water through the outlet, wherein the system is configured to vary the manner in which the valve is opened depending on the level of water determined to be inside the tank.

Preferably, the system is configured to open the valve in a manner whereby the size of the valve conduit that the water flows through is selected depending on the • level of water determined to be inside the tank. The system preferably controls the valve so as to provide a large conduit when the level of water is determined to be low and a small conduit when the level of the water is determined to be high. The valve may be controlled such that the lower the level of water is determined to be, the greater the amount by which the valve conduit is opened. In the preferred embodiments the valve is biased closed and is opened automatically at a pre-programmed time or is opened after being activated by a user. The valve is also preferably closed automatically after a predetermined period of time after having been opened.

Preferably, the valve is biased closed and the system is configured to select the length of time that the valve opens (after being activated) depending on the level of water determined to be inside the tank. The system preferably controls the valve such that when the level of water in the tank is detected as being low the valve is opened for a long time and when the level of water in the tank is detected as being high the valve is opened for a short time. The valve is preferably controlled such that the higher the level of water determined to be in the tank, the shorter the period of time that the valve is opened for. In some embodiments the valve is provided inside of the tank. In other embodiments the valve may be provided in a water pipe located outside of the tank and in fluid communication with the outlet.

The sensor for determining the level of water in the tank may have any one or combination of the features of the sensor discussed above in relation to the rainwater catchment system. As such, the sensor preferably comprises at least one of; a radar sensor for detecting the position of the water surface; a float sensor; a pressure sensor; and an electrical conductivity sensor.

The valve is preferably a flush valve for supplying water to the waste bowl of a sanitary fitting. The valve is preferably electronically controlled and may, for example, be a solenoid activated valve. Alternatively, the valve may be a mechanical valve.

The system preferably comprises a waste bowl of a sanitary fitting in fluid communication with the outlet for allowing water to exit the tank.

Specific Description

Various embodiments and an illustrative arrangement will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Fig. 1 shows a building comprising a known rainwater harvesting system;

Fig. 2 shows a building comprising a rainwater harvesting system according to a preferred embodiment;

Figs. 3A and 3B show an application of the preferred system for filling toilet cisterns; Fig. 4 shows the main components of a toilet cistern according to a preferred embodiment;

Fig. 5 shows the cistern of Fig. 4 being filled with rainwater; and Fig. 6 shows the cistern of Figs. 4 and 5 being filled with mains water.

Fig. 1 shows a building 2 having a known rainwater harvesting system. The roof 4 of the building 2 has a number of roof outlets 6 which enable rainwater collected by the roof 4 to pass into downpipes 8. The downpipes 8 channel the rainwater to an underground drainage system 10 and then into a storage tank 12. The tank 12 comprises a pump 14 for pumping the rainwater back up into the building 2 and into the toilet flushing cisterns 16 through a dedicated pipework system 18. Fig. 1 also depicts the conventional potable mains water system 20 that is supplied to the building 2.

Fig. 2 shows a building 2 having a rainwater harvesting system according to a preferred embodiment of the present invention. As in Fig. 1, the system includes a number of roof outlets 6 which pass rainwater collected on the roof 4 to downpipes 8. However, in the preferred embodiment, at least part of each downpipe 8 passes inside of the building 2 so as to allow rainwater to flow directly into a toilet flushing cistern 16. This enables the toilet cisterns 16 to be filled with rainwater as and when it rains. Various roof outlets 6 and downpipes 8 may supply rainwater to toilet cisterns 16 located on different floors of the building 2. It will be appreciated that because the rainwater is supplied directly from the roof 4 to the cisterns 16 there is no intermediate rainwater storage tank 12 as in Fig. 1. As such, there is no need to provide a large and heavy storage tank 12 which would need to be located outside of the building 2. There is therefore also no need to pump the rainwater from a storage tank 12 back up into the building 2.

Referring to Fig. 2, a mains water supply 20 is also supplied to the toilet cisterns 16 that receive the rainwater. The toilet cisterns 16 may be filled with mains water in the conventional manner. This is particularly useful during arid weather conditions during which rainfall may be insufficient to adequately supply the cisterns 16 with rainwater. A preferred embodiment of how the cisterns 16 are filled by both rainwater and mains water will be described later below with reference to Figs. 4-6. As can be seen from Fig. 2, the building 2 may also include toilet cisterns 17 that are supplied only by mains water and not by rainwater.

Each toilet cistern 16 may be used to supply water for flushing at least one toilet bowl. Figs. 3A and 3B show plan and elevation views respectively of two adjacent toilet cubicles 22,24 having toilet bowls 26 that share a communal flushing cistern 16. The cistern

16 is in direct fluid communication with the toilet bowls 26 so as to supply water directly to the toilet bowls 26 for flushing. It will be appreciated that the cistern 16 or piping 28 from the cistern 16 may be extending to supply water for flushing a third or further toilet bowl 26. This is represented by the broken lines on the right-hand side of Fig. 3B. Alternatively, the cistern 16 may supply flushing water to only a single toilet bowl 26. Although the rainwater harvesting system has been described for supplying water to toilet cisterns 16, it will be readily appreciated that the rainwater can be supplied from the roof 4 directly to other types of tanks 16. For example, the rainwater may be supplied to tanks for flushing the bowls of urinals .

Fig. 4 shows a view of a toilet cistern according to a preferred embodiment of the present invention. The cistern comprises a tank 30 for storing water, a rainwater inlet 32 for receiving rainwater from the roof 4 via the downpipes 8 and a mains water inlet 34 associated with a mains water valve 36 for controllably admitting mains water into the tank 30. The cistern tank 30 comprises a sensor 38 for determining the level of water in the tank 30. The cistern tank 30 also comprises an overflow outlet 40 for allowing water to drain out of the tank 30 when the water is, above a predetermined level. This is useful to drain excess water, for example, if there is heavy rainfall or if the mains supply valve 36 does not shut-off completely. The tank 30 also comprises a flush valve 42 at the bottom of the tank 30 for allowing water to exit the tank 30 to flush the toilet bowl 26. Two flush valves 42 are shown in Fig. 4. The right flush valve 42 illustrates a valve of the type where the valve is located internally in the tank 30. The left flush valve 42 illustrates a mechanism where the valve is located external to the tank 30. If the tank is only connected to one toilet bowl 26 then only a single flush valve 42 is required, which may be of either type illustrated in Fig. 4. If the tank 30 is for use in flushing two or more toilet bowls 26 these could be fed from the same valve 42 (e.g. for urinals) or may have separate valves 42 and flush water pipes 28 to enable them to be flushed independently.

The tank 30 also has a removable access port 44 to enable one to inspect or gain entrance into the tank 30 for maintenance. The tank 30 may also comprise a window 46 for inspecting the inside of the tank 30. The window 46 may be openable so as to operate as an access port 44.

A preferred mode of operation of the tank will now be described with reference to Figs. 4 to 6. When there is sufficient rain, the rainwater is collected on the roof 4 and flows directly into the tank 30. The rainwater enters the top of the tank through the rainwater inlet 32. The rainwater continues to fill the tank until it reaches a predetermined level, at which the overflow outlet 40 is arranged for draining excess water out of the tank 30 so as to prevent flooding from the tank 30. This is shown in Fig. 5.

If there is an insufficient supply of rainwater into the tank 30 then the level of water in the tank 30 will drop over time. This will be primarily due to opening of the flush valve 42, but may also be due to evaporation or possible leaks in the flush valve 42. In order to ensure that sufficient water is always available in the tank 30 for flushing the toilet bowl 26 a mains supply is connected to the mains inlet 34 for filling the tank 30 with mains water. The mains water supply is pressurised and has a valve 36 for selectively allowing water to enter the tank 30. The mains valve 36 is controlled by the sensor 38 within the tank 30 as follows. Referring to Fig. 6, the sensor 38 detects when the level of water in the tank 50 drops below a predetermined lower limit A and the mains valve 36 is opened in response thereto. The tank 30 is then filled with mains water until the sensor 38 determines that the level of water 50 reaches a predetermined upper limit B, at which point the mains valve 36 is closed to prevent mains water entering the tank 30. The predetermined upper limit B is preferably significantly below the maximum water storage level (i.e. the level of the overflow outlet 40) so that the use of mains water is minimised in periods of low rainfall. It has also been recognised that the higher the level of water 50 in the tank 30, the higher the pressure of the water at the flush valve 42. Consequently, the higher the level of water 50 in the tank 30, the higher the flow rate of water through the valve when the valve 42 is opened for any given time period.

Another important feature of the preferred embodiment is that when the flush valve 42 is activated to be opened, the length of time that the valve 42 is opened for is controlled depending on the level of water 50 stored in the tank. This controls the flow volume of water through the flush valve 42 and so prevents increased volumes of water being dispensed with increased water levels in the tank. This feature therefore conserves water by ensuring that a reasonably consistent volume of water is dispensed when the flush valve 42 is activated, regardless of the level of water in the tank 30.