The invention relates to an ironing board, comprising an ironing board top which, on one side, forms an ironing surface for ironing washing to be ironed thereon, and a frame for supporting the ironing board top. An ironing board of this type is well known. During use, the ironing board surface is in a horizontal position. In many cases, a steam iron is used in order to iron washing to be ironed, such as clothes, on the ironing board surface. Ironing using steam is quicker and leads to a better ironing result, in other words the ironing comfort is increased. A steam iron only has a limited capacity. The amount of water which the steam iron tank can hold is insufficient if ironing is carried out using a lot of steam and continues for a long time. As the water is used up quickly, a user has to interrupt ironing regularly in order to fill the steam iron up. Furthermore, an assembly comprising a steam iron and a steam generator is known. The steam generator is a water heater with a capacity of for example one liter or more. The steam generated which is under pressure in the water heater flows to the iron via a supply hose. As a result of the greater capacity, it is possible to iron using a lot of steam for a longer uninterrupted period of time. As a result, steam generators are becoming increasingly popular. However, steam generators cause moisture problems. The known ironing board top comprises a mesh support panel on which an absorbing layer is arranged, which is made, for example, of felt and/or flexible foam. The absorbing layer has a cushioning effect and prevents the mesh pattern of the support panel from manifesting itself at the ironing surface. The absorbing layer is substantially permeable to steam. The mesh support panel and the absorbing layer are covered by a fitted cover made of textile. The steam used will not only moisten the fitted cover, but also penetrate to below the mesh support panel. Ironing using a steam generator may then lead to moisture or even puddles of water on the floor. When the user is ironing while sitting down, droplets may furthermore land on the user's legs. An object of the invention is to provide an ironing board which reduces the risk of moisture on the floor. According to the invention, this object is achieved in that the ironing board top is provided on the side facing away from the ironing surface with a substantially moistureproof baseplate provided with a discharge opening, and in that a collecting container for collecting fluid is detachably connected to the discharge opening. The baseplate collects the steam which penetrates the ironing surface. When the steam has condensed, the water of condensation can flow to the discharge opening in the baseplate by slightly tilting the ironing board, and subsequently flow into the collecting container. Once it has been detached, the full collecting container can be emptied, for example in a sink. It is noted that an ironing board is also known which is provided with a heating coil beneath the ironing surface and a fan for sucking out moisture and/or a fan for blowing the ironing board top dry. Then, it is also possible to arrange a panel under the mesh support panel to which these components for heating, sucking and/or blowing are attached. However, such an ironing board is expensive. In addition, the service life of the components differs. A fan may already become defective after two or three years, while the frame for supporting the ironing board top usually comes with a ten-year warranty, hi addition, such an ironing board is very heavy - it weighs, for example, 25 kg or more. Furthermore, with these ironing boards, it is not known to arrange a discharge opening in the panel which opens into a collecting container. The detachable mounting of the collecting container to the discharge opening can be designed in various ways according to the invention. If the collecting container is connected to the discharge opening by means of a click-fit connection, attaching and removing the collecting container is very simple. This increases the ease of use. In this case, it is possible that the collecting container comprises a hook edge, and the baseplate comprises several resilient hook members for engaging on the hook edge of the collecting container, which hook members are arranged on the periphery of the discharge opening at a distance from one another. According to the invention, the collecting container may have an access opening which corresponds to the discharge opening, the hook edge being formed by the peripheral edge of the access opening. The discharge opening of the baseplate opens into the access opening of the collecting container. According to the invention, the collecting container may be designed in various ways, hi particular, the collecting container has a peripheral wall, which is closed at one end by a bottom and has a lid wall at the end facing away from the bottom, in which lid wall the access opening is located. In this case, the access opening may be arranged concentrically with respect to the peripheral wall, wherein the diameter of the access opening is smaller than the diameter of the peripheral wall. In the use position of the ironing board, the collecting container is under the ironing board top. In order to empty the collecting container, a user has to remove the collecting container and replace it in a "blind" manner. Positioning the access opening concentrically relative to the peripheral wall helps guide the user during this operation. It is preferable that the baseplate comprises a plastic material, such as polystyrene or polypropylene. As a result, the weight of the ironing board remains relatively low. In one embodiment, the baseplate has at least one sloping surface section for conducting moisture to the discharge opening, wherein the sloping surface section is at an angle with respect to the ironing board surface. As the baseplate is substantially flat, the water of condensation flows to the discharge opening in particular only by lifting the ironing board up at an angle. Should there be any remaining droplets near the discharge opening once the ironing board has been placed back on the floor, these can still flow into the collecting container over the sloping surface sections by the effect of gravity. In addition, the baseplate may have at least one duct for conducting moisture in the direction of the discharge opening. While tilting and otherwise handling the ironing board, the water of condensation flows through these ducts to the discharge opening. As a result, the ironing board is dry relatively quickly. In one embodiment, the ironing board top has a tapering nose section at one head end, wherein the discharge opening is arranged in that tapering nose section. In this case, it is possible to force the moisture to the discharge opening by holding the tapering nose section down at an angle. The ironing board top according to the invention may in the usual way have a mesh support panel or plate which extends between the baseplate and the ironing surface. This support panel is preferably made from expanded material. An expanded material is a mesh panel or plate which is formed by stretching a panel-shaped material until apertures appear in the material. To this end, a pattern of incisions may be provided beforehand in the panel-shaped material, such as a metal plate, which incisions extend transversely with respect to the longitudinal direction of the plate. By stretching the plate in this longitudinal direction, these incisions tear to form openings in the plate which are approximately diamond-shaped. The plate may be finished, for example re-rolled, in order to remove any deformations resulting from the stretching process. The end result is a flat plate with a mesh pattern which is produced without loss of material - as opposed to for example punching openings into the plate. In order to connect the frame effectively to the ironing board top, the baseplate is provided with two profiled sections, such as S-shaped strips, on the side facing the frame, which extend substantially parallel to one another at a distance from one another, wherein the frame has two swivelling legs, one leg being hingedly connected to the baseplate and the other leg being displaceable in the profiled sections. The invention also relates to a collecting container for use with an ironing board as described above, comprising a peripheral wall which is closed at one end by a bottom and has a lid wall at the end facing away from the bottom, in which lid wall an access opening is located which corresponds with the discharge opening. The invention will now be explained in more detail with reference to an exemplary embodiment illustrated in the drawing. Fig. 1 shows a partially cut-away perspective top view of an ironing board according to the invention; Fig. 2 shows a perspective bottom view of the ironing board shown in Fig. 1; Fig. 3 shows a perspective view of a section of the baseplate of the ironing board shown in Fig. 1 ; Fig. 4 shows a cross-sectional view of the nose section of the ironing board shown in Fig. 1 ; Fig. 5 shows a top view of a baseplate of the ironing board shown in Fig. 1. The ironing board according to the invention shown in Fig. 1 is denoted in its entirety by reference numeral 1. The ironing board 1 comprises an ironing board top 2 and a frame 3 for supporting the ironing board top 2. The ironing board top 2 has an ironing surface 5 on one side. During use, the clothes to be ironed are on the flat ironing surface 5, so that they can be ironed. The ironing board 1 furthermore comprises a support 6 which bears an assembly consisting of a steam generator 8 and an iron 9. The ironing board top 2 comprises a mesh metal support plate or panel 10 which is made of expanded material, that is to say the support plate is made by first providing a pattern of incisions in a solid metal plate, which incisions extend cross¬ wise with respect to the longitudinal direction of the plate. These incisions are then torn open by the plate being stretched in the longitudinal direction to form substantially diamond-shaped openings. The plate is re-rolled in order to eliminate any deformations which result from the stretching process. An absorbing layer 11 is arranged over the mesh metal support panel 10, which layer is made, for example of felt and flexible foam. The absorbing layer 11 has a cushioning effect so that the mesh pattern of the support panel 10 does not manifest itself at the ironing surface 5. The absorbing layer 11 is substantially permeable to steam. A fitted cover 12 is wrapped over the support panel 10 and the absorbing layer 11, which fitted cover is securely held in place by an elastic band (not shown). The fitted cover 12 and the absorbing layer 11 protect the clothes to be ironed from damage. As shown in Fig. 2 and 4, a baseplate 15 which is substantially moisture- proof is situated under the mesh metal support panel 10. The baseplate 15 is for example made of plastic material. A discharge opening 16 is cut out in the baseplate 15. In this exemplary embodiment, the discharge opening 16 is at the head end of the ironing board top 2, where a tapering nose section is formed. hi this exemplary embodiment, the baseplate 15 comprises a hook plate or panel 14 which is illustrated separately in Fig. 3. The discharge opening 16 also extends through the hook panel 14 (see Fig. 4). The hook panel 14 comprises a spacer 13 which abuts against the top of the baseplate 15. In addition, the spacer 13 reinforces the hook panel 14. Six resilient hook members or elements 17 are provided along the periphery of the discharge opening 16. Obviously, the baseplate 15 or its associated hook panel 14 may have more or fewer hook elements according to the invention. The hook elements 17 are likewise made of plastic. The hook elements 17 each have a resilient stick 18 which extends downwards from the baseplate 15. At the head end of the stick 18, which head end is remote from the baseplate, there is a hook head 19. The hook elements 17 are prestressed into the position shown in Fig. 3, in which the stick 18 extends substantially at right angles to the baseplate 15. The hook panel 14 is attached to the baseplate 15 by means of the hook elements 17. To this end, the hook elements 17 grip behind the projecting peripheral edge 30 of the baseplate 15, which delimits the discharge opening 16, as shown in Fig. 4. In this case, the spacer 13 bears against the top of the baseplate 15. In an alternative embodiment according to the invention, the hook panel is integrally formed with the baseplate. In this case, the hook panel is not a separate component and the hook elements 17 are integrally formed with the baseplate 15. According to the invention, the hook elements 17 can engage with a collecting container 20. The collecting container 20 comprises a peripheral wall 22 which is closed at one end by a bottom 21. At the end remote from the bottom 21, there is a lid wall 23 which is substantially frustoconical in shape. An access opening 25 is cut out in the lid wall 23, which corresponds to the discharge opening 16. The access opening 25 is arranged concentrically relative to the peripheral wall 20. When the user attaches and removes the collecting container by hand, he/she has a better sense of direction, which means that the user less promptly has to visually attach the collecting container while standing next to the ironing board. The collecting container 20 can co-operate with the hook elements 17. By arranging the collecting container 20 against the heads 19 and subsequently pushing the collecting container 20 towards the baseplate 15, the hook elements 17 bend slightly radially inwards. The sticks 18 of the hook elements 17 in this case act as leaf springs. When the collecting container 20 has been moved upwards sufficiently, the heads 19 of the hook elements 17 snap behind the peripheral edge 26 of the access opening 25. Li this manner, the peripheral edge 26 of the access opening 25 forms a hook edge. The collecting container 20 is then suspended from the baseplate 15. Removal of the collecting container 20 takes place in reverse order. In addition to the above-described snap or click-fit connection between the collecting container 20 and the baseplate 15, this connection may also be designed in different ways. For example, the collecting container may be screwed to the baseplate (not shown). Fig. 5 shows that there are several ducts 27 and sloping surface sections 28 in the baseplate 15 in order to conduct moisture to the discharge opening 16. The sloping surface sections 28 are formed by a section of the hook panel 14. The frame 3 shown in Fig. 1 and 2 for supporting the ironing board top 3 can swivel between a folded-in position (not shown) and a folded-out position, which is shown in Fig. 1. The frame 3 comprises two legs 30, 31 which are hingedly connected relative to one another by means of a hinge 33. The ironing board 1 is supported on the floor by means of the legs 30, 31 in a stable manner. As a means of connecting the legs 30, 31, two profiled sections 36 are arranged on the underside of the baseplate (see Fig. 2). The profiled sections 36 are in this exemplary embodiment formed by two S-shaped strips which extend substantially parallel and at a distance from one another in the longitudinal direction of the ironing board top 2. The one leg 31 is hingedly connected to the ironing board top 2 or the profiled sections 36, while the other leg 30 has two guide pins which are accommodated slidably in the respective profiled sections 36. The operation of the ironing board according to the invention is as follows. While ironing, a user moistens the washing to be ironed by means of a lot of steam in order to increase the ironing comfort. This steam ends up in the baseplate 15 via the fitted cover 12, the absorbing layer 11 and the mesh support panel 10. The steam condensates on the baseplate 15, following which the water of condensation flows to the discharge opening 16 via the ducts 27 and the sloping surface sections 28 as a result of the ironing board being held at an angle. The discharge opening 16 opens into the collecting container 20, where the moisture is collected. When a user has finished ironing, he/she can snap the collecting container 20 off the baseplate 15 in a simple manner and put it in a sink. As a result, the floor on which the ironing board 1 according to the invention stands will remain dry.