Private water supplies
The council is responsible for testing private water supplies, such as boreholes or wells, to make sure they are safe to use for drinking and washing. The cost of sampling and analysis is met by the person responsible for the supply.
If the water persistently fails tests for bacteria and chemicals then the council can insist that the owner takes action, such as installing a water treatment system.
Mains water supplies
If you are on a mains supply of water you should contact your water company if you have a problem. If you are not satisfied by the response of the water company, then you should contact the Drinking Water Inspectorate who investigate complaints and incidents that affect drinking water quality.
Blue green algae in ponds is the responsibility of the land owner or management body. In many cases the local town/parish council may have a controlling interest. Contact the Environment Agency for more information.
Water quality in swimming pools is the responsibility of the pool operator. They should be able to provide you with information about how the water is treated and when the water was tested.