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Monitoring for trace elements in drinking water - WT1254

1. Background

Routine monitoring for trace elements in drinking water is only conducted for the elements specified in the Water Supply (Water Quality) Regulations. Specified elements include antimony, arsenic, boron, cadmium, chloride, chromium, copper, fluoride, iron, lead, manganese, mercury, nickel, selenium and sodium. Monitoring for other elements will only normally be conducted in response to specific identified risk. Recently DWI has funded investigations of uranium1 and molybdenum2 in drinking water in response to recent developments in WHO guideline values. Both these studies showed a good level of compliance should the WHO guideline value be adopted as a standard. The molybdenum report also gave some data on other trace elements in drinking water which is summarised below.

Element /Limit of detection(µg/l)/ No of samples of final water /No exceeding lod / Mean of detectable conc’n (µg/l)/Max conc’n (µg/l)
Li 0.003 49 49 8.4 24.2
Be 0.003 49 25 0.37 0.16
Sc 0.05 49 49 0.93 3.09
Ti 0.04 49 49 3.62 5.97
V 0.02 49 49 0.55 2.43
Co 0.006 49 36 0.12 0.72
Zn 1 49 45 25.77 389
Rb 0.002 49 49 1.65 3.17
Sr 0.03 49 49 490 3320
Mo 0.03 49 36 0.62 1.51
Sn 0.006 49 43 0.26 5.74
Cs 0.002 49 34 0.02 0.06
Ba 0.06 49 49 62 151
W 0.01 49 11 0.04 0.10
U 0.002 49 44 0.39 1.94

The last comprehensive study on trace elements in British tap water was conducted as part of the Regional Heart Survey in the late 1970s. Summary result for this study3,4 were published in 1982 and 1987. The study analysed for 26 trace elements in about 3000 samples taken from 1000 properties supplied by 75 different sources. The summary results are expressed as source mean values, and many of the means are close to or below the limit of detection so the results are not straight forward to interpret. Typical limits of detection the time were low µg/l and since then analytical methods have improved significantly, as can be seen from the table above. The study did identify a number of elements for which the first draw sample were significantly higher than flushed samples, in some case this was due to dissolution of plumbing metals but in other case the explanation was not clear.
More recently, in 1987, a survey5 of baseline concentrations of trace metal level in filtered groundwater was conducted. The limits of detection were better than the Regional Heart survey but perhaps not as good as currently available. The results may not reflect concentrations in drinking water derived from groundwater and are unlikely to reflect concentrations in drinking waters derived from surface water.
Water companies also conduct raw water monitoring and these results are reported to DWI. Preliminary analysis suggests most of the raw water monitoring relates to elements already covered by the regulations but a few companies monitor for additional elements in raw water. A summary of the additional elements and (number of companies monitoring) is given below
Silver (4), barium (11), bromide (6),calcium (16), cobalt (2), potassium (9), lithium (3), molybdenum (1), phosphorus (8), strontium (4), vanadium (2) uranium (3) and zinc (15).
From time to time queries are raised about trace element in drinking waters about which there are limited recent data. Accordingly it is considered timely to look again at concentrations of trace element in drinking water. This will give better estimates of concentrations, provide a single point of reference for any queries on the issue and allow more accurate estimates of the contribution of drinking water to overall intakes.

The objectives are to:
1) Review existing data on trace element in drinking water and other related waters in England and Wales. Summarise the findings. Identify gaps in our current knowledge.
2) Define an analytical suite of trace elements having due regard to the gaps identified, analytical methodology and knowledge of possible presence in water
3) Make a selection of approximately 40 public drinking water supplies - the selection needs to reflect the variation in raw water types and treatment processes found in England and Wales- liaise with water companies to select sites and arrange access to appropriate sampling sites and locations.
4) Conduct a quarterly monitoring programme from water treatment works in accordance with best practice in terms of sampling and analysis, including appropriate analytical quality control.
5) Supplement the survey with additional sampling (flushed and unflushed) at consumers taps where there is a likelihood concentration may increase in distribution or within domestic plumbing.
6) All samples must reflect the quality of water drunk and so should be on final drinking waters without any additional filtration.
Time-Scale and Cost
From: 2010

To: 2013

Cost: £107,159
Contractor / Funded Organisations
British Geological Survey
Drinking Water              
Fields of Study
Water Quality