Any sample that fails to meet the maximum limits in the Private Water Supplies (England) Regulations 2016 must have an investigation to determine the reason for the failure and to identify what is needed to improve the supply. This may mean further sampling being conducted at the source, holding tanks and/or other parts of the system to assist the investigation.

If a wholesome supply cannot be achieved through implementing physical changes to the supply, the water will require treatment. A wide range of treatment options are available for both chemical and microbiological problems.

In the event of failure, where a supply is found to be 'unwholesome' or a potential 'risk to human health', a notice will be served requiring improvements and/or 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 may remain in force until either it has been complied with or by the court case.