Risk assessment


Regulation 6 England (Wales) requires a local authority to undertake a risk assessment at least every 5 years for each private water supply within their area. The purpose of the risk assessment is to establish whether there is a significant risk of supplying water that could constitute a potential danger to human health. Local authorities must also use the risk assessment process to establish whether there is a risk of non-compliance with any of the standards or indicator parameter values outlined in the Regulations. The risk assessment should also be used as part of the information to enable local authorities to consider whether it can exclude parameters from the audit monitoring requirements

In addition the local authority should review a risk assessment whenever there is any significant change in circumstances in respect of the supply system (such as the deterioration of raw water quality, installation of new treatment process etc.). For some supplies, particularly those conducted early in the first five year period where there are gaps in the information recorded, for example the Inspectorate’s tool was not used, or additional information requested was not forthcoming, the local authority may deem it prudent to visit the site and thoroughly re-assess the supply.

Conducting a risk assessment

The primary objectives of a risk assessment are to:

  • identify the risks in the catchment that affect, or could affect, the quality of the source of the private supply and any control measures that are practical to reduce the risk

  • identify the risks that need to be controlled by treatment and, if appropriate treatment is not present, installing and maintaining appropriate treatment processes to remove or reduce the concentrations of contaminants;

  • identify the risks of contamination entering the distribution network

  • identify the risks of contamination within premises

DWI has developed a number of risk assessment tools to assist local authorities in undertaking risk assessments for private water supplies as required by regulation 6 of The PWS regulations 2016. These tools can also be used for supplies to single domestic dwellings where a risk assessment has been requested.

In response to requests from local authorities for a condensed version of the risk assessment tool for use on simple systems with common types of treatment, there is also an edited version of the tool. This is listed as 'risk assessment lite' and may be typically used on supplies that consist of a single source followed by one or two stages of treatment, such as prefiltration and UV disinfection.

Please ensure you use the most up to date version of the risk assessment tool. The version number can be found on the first tab in each tool. All tools should be compatible with Excel 2010 onwards. Please contact the Inspectorate should you experience any compatibility issues.

Regulation 8 Supplies only Risk Assessement Full Tool - Regulations 8, 9, and 10 (Regulation 11 in Wales) Risk Assessment Lite - Regulations 8, 9, and 10 (Regulation 11 in Wales) Risk Assessment tool for toilet flushing
Risk assessment for PWS that originate from mains water and are classed as Regulation 8 supplies only
Full site risk assessment suitable for all private supplies
Condensed from full site risk assessment, to be used on simpler sites. May be suitable for sites requiring reassessment.
Condensed risk assessment tool for private supplies that are used exclusively for toilet flushing
V 2.05 (Excel 355KB)
Date of last update: 15/07/19
V 3.06(Excel 385KB)
Date of last update: 15/07/19
V2.10  (Excel 718KB)
Date of last update: 16/09/19

V2.03 (Excel 130KB)
Date of last update: 15/07/19

Please see guidance for RA Lite (PDF 752KB)
Please see guidance for RA Lite (PDF 752KB)

Explanatory Notes  (PDF 752KB)
Date of last update 26/11/18

Please contact us for access to the training video 


These tools are produced under licence, permitting third parties to use the risk assessment tool by local authority agreement, and without altering, copying or using it for commercial gain. The tools are therefore provided in a protected format and we cannot supply them unprotected.

DWI has also produced an Action Plan look up table (PDF 93KB) listing common mitigation measures.

Assisting the Risk Assessment

Local authorities may wish to consider gathering information regarding a private supply from the relevant person(s) ahead of any planned risk assessment. Whilst this does not replace the need for a site visit and full risk assessment, it can reduce the amount of follow up work required.

An Information Pack (Word 1.1MB) can be sent to relevant person(s) inviting them to provide details or evidence about their supply. Local authorities should take the information provided, input it into their risk assessment and then verify the information onsite. As a minimum, the information in Table 1 should be able to be provided by the relevant person(s) ahead of the local authority risk assessment. Example tables for sections, where relevant, have been included.

Risk Assessment of Single Domestic Dwellings

Whilst a local authority is not required to undertake a risk assessment to a single domestic dwelling, if the owner or occupier (including a tenant) requests this service then the Regulations require the local authority to conduct a risk assessment. The local authority can make a charge to the person making the request for this service up to the maximum specified in the Regulations

Page reviewed: 16 September 2019
Page modified: 16 September 2019

Drinking Water Inspectorate