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Private water supplies – Risk assessments and testing procedure

Risk assessments

The regulations require each supply (excluding single private domestic dwellings) to undergo a risk assessment every five years to determine how regularly the supply needs to be tested and for which parameters i.e. which types of bacteria, chemicals etc.

This involves surveying the supply, from the source through to point-of-use, to identify factors that could lead to contamination of the supply. Factors influencing sampling requirements include the type of source (borehole, well etc.), how well it is protected, the treatment methods in place, the number of people served by the supply and the intended use of the water. 

  • Larger supplies (using more than 10 cubic metres of water per day and serving 50 or more persons) and those serving commercial premises are required to undergo regular monitoring.
  • Small supplies (using less than 10 cubic metres of water per day and serving fewer than 50 persons) are monitored at least once every five years and more frequently if shown to be necessary by the risk assessment.
  • Supplies serving only an individual domestic dwelling will only be risk assessed and tested at the request of the owner or occupier.

Risk assessments will normally be carried out by prior appointment, and where possible details of what needs to be inspected/considered will be provided prior to the site visit.  This is to ensure that the owner or occupier can arrange access to the various parts of the water system, arrange for someone with detailed knowledge of the system to attend and generally reduce the amount of time we are required to be on site, thereby reducing the cost.


Samples from private water supplies will normally be taken from a consumer tap and then sent for analysis at an approved laboratory.  The sampling frequency and the extent of analysis needed will depend on the results of the risk assessment.  


Any sample that fails to meet the prescribed concentrations laid out in the regulations must be investigated to determine the reason for the failure and to identify what action is needed to improve the supply. 

This may mean further sampling being conducted at the source, holding tanks and/or other parts of the infrastructure to assist the investigation. 

If a wholesome supply cannot be achieved through implementing physical changes to the supply network, the water will require treatment before use. A wide range of treatment options are available, and these will be set out in the findings of the investigation. 


In the event of failure, where a supply is found to be ‘unwholesome’ or a ‘risk to human health’, a notice will be served either prohibiting or restricting the supply, as appropriate. The notice will be specific for each supply that has a failure of standards.

This notice can be appealed in a magistrate’s court and/or by appeal to the secretary of state, but the notice will remain in force until either it has been complied with or it is suspended by the courts/secretary of state. 


In certain circumstances where a supply fails the water quality standard, but the failure is of a parameter which does not cause a risk to health, the council may grant an ‘authorisation’ to exceed the statutory limit. This authorisation would be for a temporary period, while measures are put in place to correct the problem.

Contact us - Environmental Protection

01235 422403
(Text phone users add 18001 before dialing)

Vale of White Horse District Council
Environmental Protection Team
Abbey House
Abbey Close
OX14 3JE