Sampling and monitoring

Sampling of Private Water Supplies

DWI has developed a Scheme (Sampling Procedures) Manual to assist local authorities to comply with the ISO/IEC 17024 requirement within the Regulations*. 

Any person collecting, transporting and storing samples of private water supplies, must comply with the procedures contained in this manual. In practice, this means becoming a certified sampler.

CATG are the certification body who provide training and award certification. DWI is the owner of the Scheme.

Local authorities are advised to complete the required certification as soon as possible and as Government guidance allows. Certification became a requirement from 11th July 2020 in England and 20th November 2019 in Wales. Local authorities should contact CATG regarding the availability of courses on 01524 400632 or via their website at 

Scheme (Sampling Procedures) Manual (PDF465KB)

The Scheme Manual is a controlled document. However, it may be adapted to produce a local version, provided the following criteria are observed:

  • The order of sampling cannot be changed.
  • Microbiological methods cannot be changed.
  • Chemistry methods can be changed where they can be justified by the accredited laboratory service provider.
  • Maintain the methodology as per the scheme procedure wherever possible
  • Transportation and sample handling procedures can be tailored to the local situation, but must meet the overall regulatory requirements.
  • Methods shown in the appendices are not part of the accreditation, and are provided as examples of good practice for investigational sampling and to provide examples of record templates.
  • Other relevant local provisions such as local health and safety references or policy can be included.

Further guidance in developing local manual can be found here:  Guidance on developing private water supplies sampling manuals (PDF 26KB)

Further information on the certification scheme can be found here:  the scheme (PDF126KB).

DWI will be monitoring progress with training and accreditation, and will report on the position in our annual report to Ministers.

*The Private Water Supplies (England) (Amendment) Regulations 2018 and the Private Water Supplies (Wales) Regulations 2017 require local authorities to demonstrate that the sampling, transportation, and storage of private water supplies complies with the ISO/IEC 17024 standard. 

Sampling and monitoring for Regulation 8 supplies (private distribution systems)

The monitoring of each Regulation 8 supply must be based on the outcome of the regulatory risk assessment carried out for that supply. The relevant parameters and frequency of sampling should reflect the risk rating and the nature of the hazards identified in the risk assessment:

  • coliforms and E.coli (ingress into the network or poor hygienic conditions, especially tanks)
  • colony counts (upward trend may indicate deterioration of water quality)
  • conductivity, hydrogen ion and turbidity
  • iron and zinc (from corrosion of galvanised steel or cast iron pipes), manganese, aluminium
  • taste and odour (ingress and permeation of plastic pipes)
  • trihalomethanes and bromate (disinfection by-products) (especially if there is chlorination within the private distribution network)
  • lead, nickel and copper (from the pipe work or tap fittings in the private distribution network or within the premises
Sampling and monitoring for Regulation 9 supplies

There are two types of monitoring for Regulation 9 supplies (excluding supplies to tenanted dwellings in Wales, which fall within regulation 11 of The Regulations (Wales))

Monitoring of Group A parameters
The purpose of monitoring for Group A parameters is to:

  • determine whether or not water complies with the concentrations or values in Schedule 1 of the Regulations
  • provide information on the organoleptic (taste, odour and appearance) and microbiological quality of the water
  • establish the effectiveness of the treatment, including disinfection.

The parameters, ammonium, coliform bacteria, colony counts, colour, conductivity, E.coli, hydrogen ion concentration (pH value), odour, taste and turbidity, must be monitored in all large supplies at the check monitoring frequency.

Monitoring of Group B parameters
The purpose of monitoring Group B parameters is to:

  • determine whether or not the water complies with the concentrations or values in part 1 or 2 of Schedule 1 of the Regulations, other than Group A parameters already being sampled under part 1 of Schedule 2 (the standards and indicator parameters).
  • check (where disinfection is used), that disinfection by-products are kept as low as possible without compromising the disinfection.

The likely sources of individual parameters table (PDF 26KB) provides information on likely sources of specific parameters within a private water supply.  Criteria that could be used to decide on exclusion of a particular parameter from audit monitoring is given in the Information Note on Regulation 7 (England) (Wales).

Variation of monitoring requirements for Group A and group B parameters

A local authority may reduce the sampling frequencies required for a parameter, or cease to monitor a parameter (other than E.coli), but can only do so in accordance with the conditions specified in Part 2A of The Private Water Supplies (England) (Amendment) Regulations 2018 and Part 4 of Schedule 2 of The Private Water Supplies (Wales) Regulations 2017.


Sampling and Monitoring for Regulation 10 (England) Supplies and Regulation 11 (Wales) supplies

The Regulations require a local authority to monitor all its Regulation 10 supplies (except a supply to a single dwelling) at least every five years and more frequently if required by the risk assessment for the following parameters:

  • Conductivitya
  • Enterococci
  • Escherichia coli (E.coli)
  • Hydrogen ion (pH value)
  • Turbidity
  • Any parameter in Schedule 1 to the Regulations identified in the risk assessment as being at risk of not complying with the concentrations or values
  • Any other parameter identified in the risk assessment as a risk to human health.

A local authority may monitor a private supply to a single dwelling for the same parameters listed above if it is concerned there may be a potential danger to human health. However a local authority can only charge for this service if requested by the dwelling owner or occupier.

Monitoring of radioactive substances

Regulation 11 (England) and Regulations 12 and 13 (Wales) of The Regulations requires that a local authority must monitor each private water supply in its area for radioactive substances. In England local authorities must ensure that this is carried out in accordance with the requirement of Part 3 of Schedule 3 of The Regulations (England), and in Wales Schedule 3 of the Regulations (Wales).
Further information came be found in the Information Note for regulation 7 found here:


Page reviewed: 11 November 2020
Page modified: 11 November 2020

Drinking Water Inspectorate