The protection of the common resource "water" against pollution is generally regulated through laws and decrees (also referred to as 'command and control', 'regulatory' or 'legal' instruments). Some of these rules are:

1. "User-standards" concentrates on specifying which water is suitable for a certain use, implicitly assuming that there is a choice. A good example of this is drinking water standards. The main objective of this type of rule is the protection of consumers who are depending on a water supplier.
2. "Effluent-standards" concerns the discharge of used water. The most simple rule would be that any water used by human activity should be discharged back with the same quality as it originally had when abstracted. This would guarantee a natural water quality everywhere in the system. The main objective of this type of rule is to protect the common property from damage induced by individuals and companies.
3. "Ambient-water-standards" are intermediary type of rule. They can be considered "user-standards" when they specify the minimum quality of source water, but at the same time they limit discharges to the extent that the resulting mixed water quality is limited.

Almost every country or state presently adopted a system where "user-standards", "effluent-standards" and "ambient standards" are used in combination. These regulatory measures allow a direct control on achieving objectives and provide equity to all polluters.