Research and analysis

Drinking water quality in England: a triennial report (2020 to 2022)

Published 20 December 2024

Applies to England

Introduction

This is the second 3-yearly report on the quality of drinking water supplies in England, covering 2020 to 2022. It summarises the quality of public supplies and the largest private supplies serving more than 5,000 consumers or 1,000 cubic metres (m3) a day. The report is compiled by the Drinking Water Inspectorate, a part of Defra, who act on behalf of the Secretary of State to regulate drinking water quality in England.

This report demonstrates the high quality of drinking water in England. Of the many thousands of samples taken by water companies (water supply licensees and wholesale licensees) during 2020 to 2022, 99.98% of public supplies met the regulatory standards. Every sample that did not meet the standards was investigated and, where required, actions were put in place to protect consumers and prevent recurrence.

High-quality drinking water supplies in England are due to the work of the many stakeholders involved in drinking water treatment and distribution. The Water Safety Planning approach included in the Drinking Water Inspectorate’s drinking water legislation ensures any risks are identified and dealt with effectively before they become a problem. This approach, supported by targeted enforcement action, ensures that public health always remains a priority.

Since 2010, when legislation was introduced, the quality of private supplies has been improving, but they still lag behind the standards of the public supplies. During 2020 to 2022, the largest supplies met the regulatory standards in 94.22% of samples.

Local authorities are the regulators of private water supplies. They are responsible for carrying out a risk assessment and monitoring. They can serve notices if they determine a supply is ‘unwholesome’ and must serve a notice if they determine there’s a potential risk to human health. ‘Unwholesome’ means that the water supply does not meet regulations.

Source of tap water

Public water supplies

Approximately 99% of the population of England receive a public supply from a water company. Consumers will know whether they receive a public supply because they will be billed by a water company for their drinking water supply.

Over 14,000 megalitres of water were supplied each day to a population of nearly 58,000,000 people in England. This is equivalent to about 5,600 Olympic-sized swimming pools every day. The figures for 2020 to 2022 are shown in Table 1 and the breakdown by water source is shown in Table 2.

Table 1 – Public supply statistics for England (Chief Inspector’s report)

Year	Total population	Number of water supply zones	Total daily volume of water supplied (megalitres)
2020	56,822,463	1,590	14,225
2021	57,256,186	1,630	14,137
2022	57,907,036	1,683	14,123

Table 2 – Public supply sources by percentage volume in England (Chief Inspector’s Report)

Water source	2020 volume	2021 volume	2022 volume
Ground	27%	30%	31%
Surface	65%	64%	62%
Mixed or other	8%	6%	7%

Source: Chief Inspector’s annual report (dwi.gov.uk)

Water is abstracted from surface water (rivers and reservoirs), groundwater aquifers and mixed sources, with the largest proportion being supplied from surface water.

Before it reaches consumers’ taps, public supplies are treated to remove impurities. They’re then distributed through a network of strategic water mains and storage tanks, called service reservoirs, before local water mains carry supplies into people’s homes.

The number of water treatment works, service reservoirs and water supply zones in the public supply network in England are shown in Table 3.

Table 3 – Number of water company assets in England (Chief Inspector’s Report)

Asset type	2020: number of assets	2021: number of assets	2022: number of assets
Water treatment works	1,090	1,076	1,077
Service reservoirs	3,791	3,776	3,789
Water supply zones	1,590	1,630	1,683

Private water supplies

About 1% of the population of England have a private water supply, commonly farms or small rural communities. These consumers often abstract their water from a well, spring or borehole on private land.

As explained in the introduction, this report covers the quality of the largest private supplies, of which there are 11, serving a population of almost 300,000. These supplies are mostly used as part of a commercial or public activity, such as drinks manufacturing or hospitals.

Quality standards for drinking water

Drinking water is regulated under the Water Supply (Water Quality) Regulations 2016 (as amended) and the Private Water Supplies (England) Regulations 2016 (as amended).

Both sets of regulations include standards for a wide range of microbiological and chemical parameters, plus indicator parameters and pesticides. Many are health-based standards and contain safety margins to protect the most vulnerable members of society. Other standards ensure that water is aesthetically pleasing and acceptable to consumers.

The 2 microbiological parameters Escherichia coli (E. coli) and Enterococci should be absent from drinking water to guarantee its quality. Some parameters reflect the acceptability of water to the consumer, such as appearance, taste and odour of the water. Other chemical parameters are selected for their potential impact on human health.

Chemical parameter values are based on lifelong exposure and an average drinking water intake of 2 litres per person per day. These parameters are highly unlikely to be present in drinking water in concentrations that can cause acute health effects.

The Drinking Water Inspectorate (the Inspectorate) was established in 1990 to provide independent assurance that the water industry delivers safe, clean drinking water to consumers. The Inspectorate:

• holds water companies to account
• takes action to ensure any failures are addressed
• provides technical and scientific advice to local authorities (who are the regulators of private water supplies)

Information on the regulatory work of the Inspectorate can be found on the Drinking Water Inspectorate website.

Sampling results for public water supplies

Water companies sample water supplies throughout the supply chain to confirm water remains safe to drink and free from contamination. In addition, regulations require a random selection of consumer properties to be sampled each year. Samples are taken at the point of supply, usually the kitchen tap, and analysed to check they meet the regulatory standards.

The COVID-19 pandemic brought about many challenges for the drinking water industry, which included changing the sampling programme to comply with government guidelines. For the majority of 2020 and parts of 2021, some of the consumer tap samples were taken at surrogate sample points in the network to avoid entering people’s homes and risking spread of the virus. Therefore, data for domestic plumbing metals in particular may appear to be different to other years.

The percentage compliance for the main parameter groups is shown in Table 4.

Table 4 – Compliance measured at consumers taps and supply points for public supplies

Parameter group	2020 compliance	2021 compliance	2022 compliance
Microbiology	99.98%	99.98%	99.98%
Chemicals	99.96%	99.96%	99.94%
Indicator parameters	100%	99.98%	99.97%
Pesticides	100%	100%	100%

Drinking water supplies are generally of excellent quality and consistently meet the standards in the regulations. Each year, a small number of samples failed to meet the standards. The exact numbers of samples and failures for each parameter are shown in tables 5 to 9.

The majority of substances met the regulatory standards all the time (100% compliance). Lead (99.6%) and nickel (99.64%) had the poorest performance, followed by odour (99.80%), coliforms (99.82%), iron (99.83%) and taste (99.86%).

Table 5 – Compliance data 2020 to 2022 for microbiological parameters in zones and supply points combined

Parameter	2020 samples taken	2020 failures	2021 samples taken	2021 failures	2022 samples taken	2022 failures	Percentage compliance
E. coli	134,730	11	149,009	11	145,904	25	99.99%
Enterococci	14,757	4	12,293	4	12,387	2	99.97%

Table 6 – Compliance data 2020 to 2022 for chemical parameters in zones and supply points combined

Parameter	2020 samples taken	2020 failures	2021 Samples taken	2021 failures	2022 Samples taken	2022 failures	Percentage compliance
1,2-dichloroethane	11,714	0	10,093	0	10,082	0	100%
Aluminium	47,361	8	47,222	12	49,001	18	99.97%
Antimony	12,745	0	12,303	0	12,194	0	100%
Arsenic	12,749	0	12,294	0	12,195	1	100%
Benzene	11,729	0	10,089	0	10,083	0	100%
Benzo[a]pyrene	12,436	2	12,664	2	12,360	3	99.98%
Boron	10,727	0	10,379	0	10,132	0	100%
Bromate	11,320	0	11,257	0	10,919	0	100%
Cadmium	12,566	0	12,328	0	12,235	0	100%
Chromium	12,822	2	12,330	0	12,389	0	99.99%
Colour	71,196	0	50,598	0	53,179	0	100%
Copper	10,747	6	12,268	1	12,303	2	99.97%
Cyanide	8,272	0	7,987	0	7,642	0	100%
Fluoride	12,423	0	10,862	0	10,227	0	100%
Iron	46,849	62	47,682	101	49,437	81	99.83%
Lead	10,551	40	12,269	38	11,285	59	99.60%
Manganese	46,641	19	47,177	12	49,008	14	99.97%
Mercury	8,341	0	7,944	0	8,517	0	100%
Nickel	10,534	35	12,256	46	11,238	43	99.64%
Nitrate	41,878	1	22,788	0	22,154	0	100%
Nitrite – consumer’s taps	41,985	2	22,785	0	22,180	3	99.99%
Nitrite or nitrate formula	41,385	1	22,186	0	22,051	0	100%
Odour	46,637	89	50,591	108	53,139	103	99.80%
Polycyclic aromatic hydrocarbons	12,349	1	12,495	0	12,281	1	99.99%
Selenium	12,742	0	12,296	0	12,226	0	100%
Sodium	12,676	2	11,609	1	12,398	1	99.99%
Taste	46,564	60	50,477	53	53,045	88	99.86%
Tetra-chloromethane	13,314	0	10,894	0	11,495	1	100%
Trichloroethene and tetra-chloroethene	13,265	0	11,574	0	11,415	1	100%
Trihalomethanes	13,314	1	12,270	2	12,390	0	99.99%
Turbidity	71,564	6	50,575	4	53,175	8	99.99%

Table 7 – Compliance data 2020 to 2022 for indicator parameters in zones and supply points combined

Parameter	2020 samples taken	2020 failures	2021 samples taken	2021 failures	2022 samples taken	2022 failures	Percentage compliance
Ammonium	57,166	0	37,571	1	36,683	0	100%
Chloride	13,014	3	10,390	4	10,233	6	99.96%
Clostridium perfringens	24,684	4	27,097	7	23,977	6	99.97%
Coliform bacteria	134,730	149	149,007	282	145,911	342	99.82%
Colony counts after 3 days at 22°C	60,903	0	59,715	0	59,234	0	100%
Conductivity	79,287	0	63,230	0	62,435	0	100%
Hydrogen ion (pH)	71,270	1	53,914	4	53,199	3	100%
Sulphate	13,331	0	34,233	0	10,248	0	100%
Total indicative dose (gross alpha and beta)	0	0	1,996	0	2	0	100%
Total organic carbon	8,472	0	8,742	0	8,745	0	100%
Tritium	353	0	438	0	316	0	100%

Table 8 – Compliance data 2020 to 2022 for pesticides in zones and supply points combined

Parameter	2020 samples taken	2020 failures	2021 samples taken	2021 failures	2022 samples taken	2022 failures	Percentage compliance
Individual pesticides	161,584	3	164,028	0	171,746	3	100%
Special pesticides	14,924	0	14,603	0	16,677	0	100%
Total pesticides	7,147	0	7,141	0	7,297	0	100%

Table 9 – percentage of samples not meeting the standard

Parameter	2020 failures	2021 failures	2022 failures
Lead	0.38%	0.31%	0.52%
Nickel	0.33%	0.38%	0.38%
Coliform bacteria	0.11%	0.19%	0.23%
Odour	0.19%	0.22%	0.20%
Fluoride	0%	0%	0%
Taste	0.13%	0.11%	0.17%
Iron	0.13%	0.21%	0.16%
Chloride	0.02%	0.04%	0.06%
Clostridium perfringens	0.02%	0.03%	0.04%
Aluminium	0.02%	0.03%	0.04%
Manganese	0.04%	0.03%	0.03%
Benzo[a]pyrene	0.02%	0.02%	0.02%
E. coli	0.01%	0.01%	0.02%
Copper	0.06%	0.01%	0.02%
Enterococci	0.03%	0.03%	0.02%
Turbidity	0.01%	0.01%	0.02%
Nitrite – consumer’s taps	0%	0%	0.01%
Trichloroethene and tetra-chloroethene	0%	0%	0.01%
Tetra-chloromethane	0%	0%	0.01%
Arsenic	0%	0%	0.01%
Polycyclic aromatic hydrocarbons	0.01%	0%	0.01%
Sodium	0.02%	0.01%	0.01%
Hydrogen ion (pH)	0%	0.01%	0.01%
Trihalomethanes	0.01%	0.02%	0%
Chromium	0.02%	0%	0%

Lead

The lead failures come from lead plumbing, which is present in some older buildings. Water companies treat drinking water with phosphate to provide a coating within lead pipes. While this reduces the amount of lead that dissolves into the water, it is not completely effective.

Water companies are tackling lead failures using a risk-based approach, prioritising schools and vulnerable consumers. The Inspectorate has published research on long term strategies to reduce lead exposure from drinking water.

Nickel

Nickel failures are sometimes found to be associated with the installation of new water fittings in the home, such as new chrome taps. The nickel leaching from these products is often attributable to chrome, nickel or nickel-plated products and is variable depending on the plating process

The Inspectorate and UK Water Industry Research body (UKWIR) are carrying out research to find a possible methodology for quality assurance testing by water fittings manufacturers.

Find more information about approval of products for water fittings on the Inspectorate’s website.

Check the WaterSafe website for advice on finding approved plumbers.

Coliforms

Coliforms are extremely common on surfaces and are used as an indicator of environmental contamination. In each case, an investigation is carried out to investigate the cause and resamples are taken until the issue is resolved.

Most coliform failures were traced to the kitchen tap, which highlights the need for consumers to keep the tap clean. Few of the remaining failures were attributable to any conclusive cause.

Iron and manganese

Iron and manganese can be found in tap water as these metal deposits can accumulate in the pipe network. These deposits can come from a variety of sources.

Iron and manganese are found naturally in source waters, and iron is used in the treatment process at water treatment works. Water companies will try to reduce the amount of iron and manganese leaving treatment works so these metals do not ‘seed’ the network.

Unlined cast iron pipes can also be a source of iron. Corrosion of the metal pipe wall can happen over time and depending on the water chemistry.

The mains sediments can collect in pipes. If there is a sudden change in water flow or direction, these mains deposits can become disturbed and make their way through to the consumer’s tap. For example, this could happen after a burst main or if the water company needs to re-route water around the network.

When this happens, consumers can sometimes experience discoloured water, which may be brown, black or orange. While often not harmful to health at the concentrations seen, receiving discoloured water is visually not appealing and can lead to rejection of the water.

Water companies will manage the concentrations of iron and manganese in the network by:

• using tighter controls at the treatment works
• carrying out maintenance on the network, such as conditioning and flushing pipes and replacing ageing pipes

Taste and odour

Taste and odour issues can be associated with consumer plumbing. Half of the taste samples and a third of the odour failures were found to be caused by deficiencies in the domestic plumbing.

Other causes of taste and odour include algal breakdown products from rivers or reservoirs in the catchment. Where repeated failures occurred, the Inspectorate has acted alongside companies to install treatment to remove taste and odour.

Pesticides

A limit of 0.1 micrograms per litre applies to individual pesticides in drinking water. This extremely low limit means that consumers are normally protected, even where marginal failures occur.

Individual pesticide failures occurred for several herbicides including metazachlor, mecoprop and propyzamide, which are all weed killers, and for metaldehyde, which is found in slug pellets. The failures are shown in Figure 1.

Catchment management is the most effective way of avoiding pesticides from entering water courses. This can be seen to have been effective for reducing the number of metaldehyde failures to just one over the 3 year period from 2020 to 2022.

Farmers and landowners working in partnership with water companies are encouraged to apply pesticides safely. This minimises the mobility of pesticides and the likelihood of them reaching the source water. Many pesticides are effectively removed by treatment with activated carbon or ozone.

A ban on metaldehyde was introduced in England. From 31 March 2021, no further sale was allowed, and all use was banned by 31 March 2022. There will be historical chemicals within the soil that will be released into the catchment over time and companies need to remain vigilant.

Figure 1 – Details of individual pesticide exceedances in England

Individual pesticide	2020 failures	2022 failures
Metazachlor	0	1
Metaldehyde	1	0
Mecoprop (MCPP)	1	0
Propyzamide	1	2

Further information on the assessment of water company performance can be found in the Chief Inspector’s annual report (dwi.gov.uk).

Sampling results for private water supplies

Private supplies in England, in common with many areas of the world, are variable in quality. Although many are excellent, compliance with the regulatory standards is worse than public supplies. Local authorities are the regulators of private water supplies.

While this report concentrates on the largest private supplies, further information on all private water supplies is available in the Chief Inspector’s annual report on private supplies (dwi.gov.uk).

A large private supply is defined as one that supplies a population greater than 5,000 or produces more than 1,000 m3 per day. All the large private supplies have had a risk assessment carried out by the local authority. This determines the quality of the supply and identifies remedial actions required for improvement.

Statistics for the large private supplies are shown in tables 10 to 12.

Table 10 – Private water supply statistics in England

Year	Total population	Total volume of water (megalitres)	Number of private supplies (approximate)	Private distribution supplies	Large, commercial and public use supplies	Single dwelling supplies	Total local authorities with private supplies
2020	828,257	235	36,913	196	7,384	2,933	253
2021	821,152	380	34,302	232	8,534	32,979	252
2022	956,429	513	34,904	417	9,400	32,934	254

Table 11 – Private water supply sources by percentage volume

Water sources	2020 volume	2021 volume	2022 volume
Groundwater supplies	61.7%	62.3%	62.6%
Surface water influenced supplies	23.1%	31.5%	30.3%
Mains water	11.2%	0.7%	0.7%
Rainwater	0%	0.1%	0%
Other	0%	0%	0%
Unknown	4%	5.4%	4.9%

Table 12 – Percentage compliance for large private supplies

Parameter group	2020 compliance	2021 compliance	2022 compliance
Microbiology	99.63%	100%	100%
Chemicals	97.74%	100%	50%
Indicator parameters	96.17%	100%	98.65%
Pesticides	100%	Not applicable	Not applicable

The numbers of samples and failures for each parameter for the large private supplies are shown in Table 13 to 16.

Table 13 – Compliance data 2020 to 2022 for microbiological parameters in large private supplies

Parameter	2020 samples taken	2020 failures	2021 samples taken	2021 failures	2022 samples taken	2022 failures	Percentage compliance
E. coli	247	1	1	0	3	0	99.60%
Enterococci	24	0	1	0	6	0	100%

Table 14 – Compliance data 2020 to 2022 for chemical parameters in large private supplies

Parameter	2020 Samples taken	2020 failures	2021 Samples taken	2021 failures	2022 Samples taken	2022 failures	Percentage compliance
1,2-dichloroethane	18	0	0	0	0	0	100%
Aluminium	75	0	0	0	0	0	100%
Antimony	42	0	0	0	0	0	100%
Arsenic	42	0	1	0	0	0	100%
Benzene	17	0	0	0	0	0	100%
Benzo[a]pyrene	14	0	0	0	0	0	100%
Boron	46	0	1	0	0	0	100%
Bromate	18	0	0	0	0	0	100%
Cadmium	42	0	0	0	0	0	100%
Chromium	17	0	0	0	0	0	100%
Colour	138	0	1	0	0	0	100%
Copper	47	0	1	0	0	0	100%
Cyanide	16	0	0	0	0	0	100%
Fluoride	19	0	1	0	0	0	100%
Iron	118	4	0	0	0	0	96.61%
Lead	43	0	1	0	0	0	100%
Manganese	118	7	0	0	0	0	94.07%
Mercury	24	0	0	0	0	0	100%
Nickel	43	1	0	0	0	0	97.67%
Nitrate	147	11	1	0	1	1	91.95%
Nitrite – consumer’s taps	146	1	1	0	0	0	99.32%
Nitrite or nitrate formula	90	11	0	0	1	1	86.81%
Odour	135	3	1	0	1	0	97.81%
Polycyclic aromatic hydrocarbons	16	0	0	0	0	0	100%
Selenium	42	0	0	0	0	0	100%
Sodium	80	0	2	0	0	0	100%
Taste	127	5	1	0	1	0	96.12%
Tetra-chloromethane	18	0	0	0	0	0	100%
Trichloroethene and tetrachloroethene	19	0	0	0	0	0	100%
Trihalomethanes	16	0	0	0	0	0	100%
Turbidity	173	0	1	0	0	0	100%

Table 15 – Compliance data 2020 to 2022 for indicator parameters in large private supplies

Parameter	2020 samples taken	2020 failures	2021 samples taken	2021 failures	2022 samples taken	2022 failures	Percentage compliance
Ammonium	106	0	100	0	0	0	100%
Chloride	32	0	53	0	31	0	100%
Clostridium perfringens	33	0	53	0	33	0	100%
Coliform bacteria	245	2	1	0	3	2	98.39%
Colony counts after 3 days at 22°C	231	0	1	0	0	0	100%
Conductivity	178	0	1	0	0	0	100%
Hydrogen ion (pH)	178	39	1	0	0	0	78.21%
Sulphate	52	0	53	0	49	0	100%
Total organic carbon	15	0	52	0	32	0	100%
Tritium	0	0	0	0	0	0	Not applicable

Table 16 – Compliance data 2020 to 2022 for pesticides in large private supplies

Parameter	2020 samples taken	2020 failures	2021 samples taken	2021 failures	2022 samples taken	2022 failures	Percentage compliance
Pesticides (individual)	24	0	0	0	0	0	100%
Pesticides (special)	0	0	0	0	0	0	Not applicable
Pesticides (total by calculation)	0	0	0	0	0	0	Not applicable

The most common failures for these largest supplies are manganese (94.07%), nitrate (91.95%), nitrite or nitrate formula (86.81%) and pH (78.21%)

This profile is not indicative of all private supplies, and in smaller supplies faecal contamination is one of the most common problems. In 2022, 3% of samples from all private supplies contained E. coli and 5.1% contained Enterococci. Failures of these 2 standards mean that the water supply is contaminated with faecal matter and there is a risk that harmful pathogens will also be present. Smaller supplies are discussed in more detail in the Chief Inspector’s annual report on private supplies (dwi.gov.uk).

The Inspectorate provides an advisory service through its website and a public phone enquiry line to:

• local authorities
• private supply owners
• the industry associated with private supplies

The Inspectorate also provides a private supply risk assessment tool, which is widely used by local authorities and their contractors.

Sampler certification became a requirement from 11 July 2020 in England and 20 November 2019 in Wales. The sampling procedures manual (dwi.gov.uk) is the reference document for ISO 17024 accreditation of local authority samplers.

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

Maintaining standards into the future

This report shows what can be achieved through effective water safety planning, compliance assessment and targeted regulation, to deliver high quality drinking water in England.

As enforcers of the regulations for public supplies, the Inspectorate will continue to work with water companies and regulators. They will ensure that catchments, water treatment works and distribution networks can meet the challenges of the future, including climate change, contamination and population growth.

The Inspectorate will also continue to supply scientific and technical advice to local authorities, private supply owners and the associated industry. Through this work, the industry will pass on a sustainable and high-quality water supply to future generations.