This applies to large private supplies of ten cubic metres or more (10m3 or 2200 gallons) per day, and to private supplies where the water is used for a commercial activity or to public premises. For these supplies, we're required to undertake a risk assessment of each supply within five years. We're also obliged to carry out check sampling for up to 17 parameters, and audit sampling for up to 46 microbiological and chemical (including pesticides) parameters, at a frequency determined by the daily volume of supply.

Commercial activity also includes holiday lets and tenanted properties.

Table of classifications

*Sample frequency can be increased depending on the outcome of the risk assessment.

This applies to any supplies which provide an average daily volume of fewer than ten cubic metres (10m3 or 2220 gallons per day), excluding supplies to a single dwelling. For these supplies we're required to undertake a risk assessment of each supply within five years, and carry out check and audit sampling at least once every five years, or more frequently if the risk assessment shows that it's necessary.

This applies to a private supply that serves a single private dwelling not being used for a commercial activity. We'll sample these supplies and carry out a risk assessment if the owner or occupier of the dwelling asks us to.

These convey water to individual premises within a site, for example holiday campsites, caravan parks, private estates etc. In such cases, the site owner or manager, not the water undertaker, is responsible for the supply, which is provided to premises through a private distribution system, and for the quality of the water supply at consumers' taps.

Such systems aren't monitored by water companies as part of their compliance monitoring programme. The regulations apply to the water supply from the point at which a water undertaker’s responsibility ceases, and the distribution system from that point becomes a 'private distribution system' under the regulations. For these systems we're required to sample in accordance with a sampling programme, to be decided by the results of the risk assessment.

The regulations impose a duty on local authorities to carry out a risk assessment on all supplies, with the exception of those serving a single domestic dwelling, within five years from 1 January 2010, and subsequently every five years.

The risk assessment process involves one of our officers visiting the PWS and physically inspecting the source, catchment, water intake, storage and treatment systems, together with visible parts of the distribution system. Other relevant details, such as persons responsible for the supply, consumers of the supply and maintenance are also recorded.

A number of questions relating to potential hazards that can affect the quality and safety of the water supplied must be answered before, during or after the risk assessment site visit.

The risk assessment determines the likelihood of the hazard resulting in a risk, and the severity of its consequences. Most likelihood scores and all of the severity scores are already pre-loaded into tables provided by the Drinking Water Inspectorate (DWI), which designed the risk assessment tool used. Risk levels high, medium and low are determined by multiplying the likelihood score of the hazard indicator by its severity. The risk levels provide a way of prioritising actions that should be carried out on the PWS to reduce the contamination risk posed by any identified hazards.

Other factors, eg sampling and analysis results, local geology and site history are also considered as part of the risk assessment process.

Relevant action points are determined, based on all the information gathered, which much be undertaken to address the identified risks to the PWS. This will help to ensure that the water supplied to consumers is safe. Any actions that need to be taken will be checked by an officer during subsequent visits to the PWS. Action points could change each time a risk assessment is carried out.

Should a water sample fail bacteriological or chemical standards, we're required to undertake an investigation to determine the cause of the failure, and in the case of a supply which is a potential danger to human health to serve a notice to specify what steps must be taken to protect human health. Informal help and advice will be given in all cases.

Where a private supply is unwholesome only because of a failure of one of the chemical parameters, we have the power to grant an ‘authorisation’ to allow the supply to continue to be used as a temporary measure for no more than three years while remedial action is taken. An authorisation can only be granted if the supply isn't a potential danger to public health, and the supply can't be maintained by any other reasonable means.