To perform the effective sanitation control of water in proper timing using a proper cleaning means by monitoring the amount of microorganisms contained in water by simple technique.

The amount (N) of ATP (adenosine triphosphate) in water is measured and the sanitation control of water is performed using the amount (N) of ATP as an index. The amount (N) of ATP is measured by measuring luminous quantity (L1) at the time of addition of an ATP extractant, luciferin and luciferase to water or measuring luminous quantity (L2) at the time of the addition of the ATP extractant, luciferin and luciferase after the addition of an ATP eliminating reagent to water. When the amount (N) of ATP reaches a predetermined value or above, a predetermined cleaning means is applied to water. When the difference between the luminous quantity (L1) and the luminous quantity (L2) is a predetermined value or below, a sterilant is preferably added as the cleaning means. This sanitation control method is suitably adapted to spring water, bathtub water, cooling tower water of a building or the like.