The importance of water quality and water treatment for private water supply Louise Ander and Rebecca Close

Rural Cornwall, where many residents use private water supplies
Joint research from the British Geological Survey (BGS) and Public Health England (PHE) has provided new information on the incidence rate of private water supply users using drinking water with high concentrations of some naturally occurring chemicals in Cornwall, UK.

Louise Ander (BGS) and Rebecca Close (PHE) briefly describe this joint study between the two organisations which was designed to fill a gap in knowledge spanning this area of public health and environmental sciences.

Our study has re-emphasised the importance of householders being aware of their tap water chemistry, and treating to improve it where necessary.

Why did we sample in Cornwall?

There are many people in rural Cornwall who use private water supplies, rather than the mains public water supply. When a private water supply is used only for a single domestic household, it is the choice of the householder(s) as to whether they test the quality of water and treat it. This means that, unlike public supplies, there is little systematic understanding of what the chemical quality of drinking/cooking water may be at the tap of householders using private water supplies.

Natural geological properties of the various rocks which are found in Cornwall means there is the potential for high groundwater concentrations of potentially harmful elements, which may be exacerbated in some areas by the impacts of historical ore extraction and smelting.  Thus, this environmental legacy, combined with the large number of single domestic households using private water supplies, meant that  the possible impacts on public health of chemical quality of private water supply in Cornwall were worthy of further investigation.

Where did we sample?

We visited ~500 properties across Cornwall, where householders had volunteered to be part of our study. We collected the small-volume samples required for laboratory analysis and measured properties such as water temperature and acidity (pH) at the tap.  The participants were provided with feedback about their water chemistry, and guidance if concentrations exceeded those in the English water quality standards.

Images from L-R: (a) Measuring pH and conductivity at the tap; (b) householder with an iron-coated old particulate filter from their domestic treatment system; (c) example of part of a domestic treatment system. 
We would like to thank, once again, all the participants in the study. Without their willingness to volunteer for our visit to collect tap water samples and treatment system information, and sometimes groundwater samples as well, we could not have arrived at the new understanding we now have of chemical properties of private water supplies. 

How does this help other private water supply users in Cornwall?

We designed the study with a ‘random’ sampling approach. Use of the word ‘random’ here is in its statistical sense, and means that we can use the results from the participating households to make predictions about outcomes where we didn’t collect and analyse a sample. For instance, if we find that 5% of households exceed a particular chemical water quality standard in our ~500 households, we infer that the overall Cornish exceedance for that chemical at household taps where private water supply from groundwater is used, may be expected to be 5%.

As we specified to the participants, this study only considered 25 chemical parameters for which there are water quality standards. Where UK standards do not exist, we cited World Health Organization, WHO, guideline values. These chemical parameters are not the only quality standards relevant to drinking water, and users should familiarise themselves with their supply’s quality in relation to the wider suite of regulation parameters, including microbiological properties.

What did we find?

We found that 65% of households exceeded one or more chemical drinking water quality standards. Of particular note are those percentage exceedances which relate to health-based chemical quality standards, especially nitrate (11%) and arsenic (5%). The maximum measured arsenic concentration was 440 µg/L, which is considerably above the drinking water quality standard of 10 µg/L. Whilst the national manganese water quality standard is set on aesthetic grounds (e.g. visible particulates in water, unpleasant taste), some of the 12% of tap waters which exceeded that value had a measured concentration which was above the WHO health-based guideline value.

Why is it important for householders to have their water tested?

Arsenic and nitrate (and some other potentially harmful chemicals) are tasteless and colourless in water. This means that you will only find out you have higher concentrations than is desirable if you commission analysis of your tap water.

This is in contrast to chemicals such as iron and manganese, which will typically cause visible sediment to form, or impart a discoloration, odour or taste to water when at high concentrations.

Treatment of domestic tap water

Treatment options suitable for installation in domestic contexts are available, and these will need to be tailored to the specific chemical (or other) quality parameter(s) that require treatment. We do not endorse any specific products, suppliers or fitters – but you may be able to access a list of useful contacts from your local authority (the regulator for private water supplies) if you have a private water supply in the UK.

Our study did show that successful treatment to decrease high concentrations of chemicals such as arsenic, iron and manganese is being achieved in some of the participant households. There were also examples of successful treatment of low pH values, which is beneficial in decreasing corrosion of metal pipes and tanks in domestic plumbing systems.

We would like to take this opportunity to reiterate the importance of treatment system maintenance, in order for the systems to work as they are intended and have the benefit to water quality that is expected. For instance, we found that 31% of the properties which self-reported the use of treatment to correct low pH water, had pH values below the lower water quality threshold value of 6.5 when we sampled them. Very few households reported treatment to decrease nitrate concentrations in tap water, but of those that did 40% were demonstrably not working effectively, and thus were presumably not achieving the outcome expected or assumed by the householders.

What next?

The project outputs will continue as we continue to learn and publish more from the collected data. These activities will include predictions of the numbers of private water supply users in Cornwall using tap water with key chemicals above drinking water quality standards, and spatial variation in groundwater chemistry.

This study was the precursor to the ongoing arsenic biomonitoring study (BGS, PHE and the University of Manchester) which is also in the process of publication – you can read more on the project website.

Further information

The scientific paper has been published open-access, so it is free of charge for anyone to read or download. The reference is:

Ander, E L, Watts, M J, Smedley, P L, Hamilton, E M, Close, R, Crabbe, H, Fletcher, T, Rimell, A, Studden, M, and Leonardi, G. 2016. Variability in the chemistry of private drinking water supplies and the impact of domestic treatment systems on water quality. Environmental Geochemistry and Health, 1-20. DOI: 10.1007/s10653-016-9798-0.

You can learn more about activities and outputs from this survey of private water supplies by looking at our website. This website includes the guidance provided to householders with chemical concentrations above the English private drinking water quality standards. The webpage will be updated as future outputs become available. We also provide external links to some of the governmental private water supply drinking water quality guidance and information which is available for the UK. If you are a Cornish resident, you will find local information on the Cornwall Council webpage.


kamal mondal said…
very helpful info about water.thanks