Variability in the chemistry of private drinking water supplies and the impact of domestic treatment systems on water quality

Abstract

Tap water from 497 properties using private water supplies, in an area of metalliferous and arsenic mineralisation (Cornwall, UK), was measured to assess the extent of compliance with chemical drinking water quality standards, and how this is influenced by householder water treatment decisions. The proportion of analyses exceeding water quality standards were high, with 65 % of tap water samples exceeding one or more chemical standards. The highest exceedances for health-based standards were nitrate (11 %) and arsenic (5 %). Arsenic had a maximum observed concentration of 440 µg/L. Exceedances were also high for pH (47 %), manganese (12 %) and aluminium (7 %), for which standards are set primarily on aesthetic grounds. However, the highest observed concentrations of manganese and aluminium also exceeded relevant health-based guidelines. Significant reductions in concentrations of aluminium, cadmium, copper, lead and/or nickel were found in tap waters where households were successfully treating low-pH groundwaters, and similar adventitious results were found for arsenic and nickel where treatment was installed for iron and/or manganese removal, and successful treatment specifically to decrease tap water arsenic concentrations was observed at two properties where it was installed. However, 31 % of samples where pH treatment was reported had pH < 6.5 (the minimum value in the drinking water regulations), suggesting widespread problems with system maintenance. Other examples of ineffectual treatment are seen in failed responses post-treatment, including for nitrate. This demonstrates that even where the tap waters are considered to be treated, they may still fail one or more drinking water quality standards. We find that the degree of drinking water standard exceedances warrant further work to understand environmental controls and the location of high concentrations. We also found that residents were more willing to accept drinking water with high metal (iron and manganese) concentrations than international guidelines assume. These findings point to the need for regulators to reinforce the guidance on drinking water quality standards to private water supply users, and the benefits to long-term health of complying with these, even in areas where treated mains water is widely available.Electronic supplementary materialThe online version of this article (doi:10.1007/s10653-016-9798-0) contains supplementary material, which is available to authorized users.

Hazard Ranking Method for Populations Exposed to Arsenic in Private Water Supplies: Relation to Bedrock Geology

“…The rationale for the sampling design aimed to lead to an effective public health management approach, by integration of environmental (bedrock) and public health (concerning population groups) information for assessment of water results, as part of an EPHT proof of concept study. A SBGC was devised to approximate the geological features across areas sufficiently large to characterise potential population exposure to chemicals via DW, as described in Ander et al [ 30 ]. The Cornwall area was divided into nine broad geological categories, defined on the basis of rock types (igneous/metamorphic/sedimentary), mineralogical characteristics (e.g., sulphide-bearing/slaty) and stratigraphy (age and therefore likely provenance).…”

“…In east Cornwall, a local newspaper advertisement was also used by the county council. After recruitment for each phase, households that volunteered for the study had their PWS DW sampled in spring (March/April) in 2011 or 2013 and measured for As and a broad suite of 55 elements and other chemical parameters, including anions by ion chromatography, pH/alkalinity and conductivity [ 30 ].…”

“…Cornwall, in south west England, is known to have geologically enhanced As concentrations due to the presence of natural Cu-Sn-Zn-As mineralisation of rocks, which has been locally exacerbated by historical mining and ore processing activities. A water sampling programme of 497 small domestic PWS supplying 508 households was conducted in Cornwall during 2011–2013 and found that up to 35% of supplies had exceedances of one or more prescribed concentration or value (PCV) of a range of chemicals and that 20% of households had one or more exceedance of health-based values for drinking water (DW), including 12% above the manganese PCV [ 30 , 31 ]. Six percent of households failed the As PCV: the PCV and WHO guideline value [ 32 ] for As in PWS is 10 μg/L [ 32 , 33 ].…”

Prolonged exposure to arsenic in UK private water supplies: toenail, hair and drinking water concentrations

“…This resulted in 127 drinking water samples collected either 31 (n ¼ 51) or 8 (n ¼ 76) months apart depending on whether households were in east (2011 initial collection) or west (2013 initial collection) Cornwall, respectively. Point-of-use drinking water samples were collected using a previously reported protocol 11 Biomonitoring. Biomonitoring was conducted on one occasion onlyat the time of the follow-up drinking water collection in November 2013.…”

“…Drinking water samples were analysed using a previously reported method. 11 Rinse solutions were diluted Â2 and analysed by a method used previously 11 for water samples. Those with visible suspended particulate were passed through a 0.45 mm Acrodisc® syringe lter (PALL Life Sciences, USA).…”