Report No DWI0757
EFFECTIVENESS OF POINT OF USE DRINKING WATER DEVICES
Final Report to The Scottish Office, Agriculture, Environment and Fisheries Department
The Scottish Office is currently undertaking a review of the Private Water Supplies (Scotland) Regulations 1992 and associated guidance notes. Local Authorities (i.e. District and Islands Councils, post 1 April 1996 the new unitary councils) offer advice on treatment of supplies, and in some circumstances point of use treatment may be appropriate. This study was undertaken to attempt to secure data on the long-term performance of point of use treatment in order to help inform the revision of the guidance notes.
The objectives of the study were to undertake a market survey on the prevalence, cost, consumer demand, life expectancy and flow rates of point of use devices; to obtain performance data; to recommend forms of device for value for money in relation to type of water quality failure and to consider the need for fail-safe mechanisms.
This report provides general information on types of point of use device and the problems they can treat. The results of the market survey are presented and analysed in terms of consumer demand, effectiveness, flow rates, technical and performance data and costs. Fail-safe mechanisms are considered and gaps in the data are identified. Recommended good practice is given for the specification, installation and maintenance of point of use equipment.
The main conclusions from the study are that manufacturers' claims are often imprecise and there are few data on performance based upon objective testing. However, Local Authority records indicate that point of use treatment can be effective provided that the devices are correctly installed and maintained; water quality failures arise almost invariably from lack of essential maintenance. Consumer demand is greatest for ultraviolet (UV) systems for disinfection and ion exchange units to remove nitrate. The total take-up of point of use equipment in Scotland for treatment of private water supplies is estimated to be in the range 4000 to 20 000 units. Provided they are maintained, point of use devices can treat an adequate flow rate of water and can be considered to be cost effective. Warning systems are preferable to fail-safe shut-down to indicate failure of point of use devices.
Point of use devices should be selected, installed and maintained in accordance with good practice and the report provides guidance on this. UV systems, with prior filtration, are recommended to deal with microbiological problems, and ion exchange units for nitrate reduction. These devices should be fitted with mechanisms to monitor performance and warn the user of failure. Local Authorities should keep records of installed point of use devices in registers of private water supplies. Users should be advised by Local Authorities on the need for maintenance and other issues, and official guidance in the form of a "layman's guide" could be helpful in this respect.
Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.