DETERIORATION OF WATER QUALITY IN DISTRIBUTION SYSTEMS PHASE I - MONITORING WATER QUALITY DETERIORATION IN DISTRIBUTION SYSTEMS FINAL REPORT - ER 206E DoE Contract PECD 7/7/120
Report No DWI0011

JUL 1986

SUMMARY

I OBJECT

The primary objectives defined in Phase I of this contract are as follows:

  1. Develop a method of measuring the quality of water as perceived by consumers.

  2. Compare the perceived quality of water with the requirements of the EC Directive relating to the Quality of Water intended for Human Consumption and the Water Industry's standards of service relating to perceived quality, and consider any implications to legislation and the Industry.

  3. Investigate the relationship between consumer satisfaction, water quality, and condition of the distribution system to enable an indication to be made of when mains maintenance is required.

Phase II of the contract concerns the pH of water following relining with cement mortar and will be reported separately.

II REASON

Discoloured water at the consumer's tap is responsible for a major proportion of complaints about quality of water supplies. Certain determinands within the EC Directive are defined for the reason of minimising consumer dissatisfaction. However in view of the way discoloured water manifests itself and its transient nature there is some concern that the parameters defined in the Directive and the procedures currently adopted to assess compliance may not be the most appropriate to ascertain whether discoloured water is occurring at the consumer's tap.

Phase I of this work has therefore been undertaken to find which determinands offer the best measure of water quality as perceived by the consumer and to develop a technique or procedure by which discoloured water problems might be better assessed.

III CONCLUSIONS

  1. The filter colour index is a good, objective method of measuring consumer perceived water quality.

  2. The chemical parameters normally used to reflect aesthetic water quality (Fe, Mn, Al, turbidity and colour) do not relate to the discolouration as measured by filter colour.

  3. The Automatic Liquid Filtration Instrument (ALFI), as it is a semi-continuous monitor of discolouration, makes it possible to:

    1. identify both persistent and transient problems, and

    2. distinguish between discolouration problems caused by poor treatment and those caused by corrosion of unlined cast iron mains.

  4. A study of the internal condition of mains in an area will not necessarily indicate the potential for discolouration problems. A far better indication can be given by the flushing of hydrants. The strength of discolouration of the flushed water and the length of time for this to clear gives a reasonable impression of the potential for discolouration under disturbed flow conditions.

IV RECOMMENDATION

The use of the filter colour parameter should be considered as an alternative to chemical analyses when assessing whether remedial work to improve discoloured water problems is necessary or has been effective.

V RESUME OF CONTENTS

The problem of discolouration is outlined giving the reasons for its occurrence in distribution and the manner in which monitoring is undertaken to minimise the risk. The currently available determinands are reviewed in terms of their ability to assess the consumer's perception of water quality.

Filter colour is proposed as an alternative determinand to chemical analysis to better reflect the consumer's perception of their water quality and the rationale behind this given.

Discoloured water problems are often transient in nature and therefore difficult to detect from spot sampling. A need has been identified for a continuous or semi-continuous measure of discolouration and an instrument (ALFI) which fulfils this requirement is described.

The investigational procedure used at a number of sites to evaluate the ALFI is presented and the results are given in site by site summaries in Appendix A.3.

The results from all 15 study sites are analysed together to compare the consumer reaction to supply with the measured water quality and to compare the filter colour determinand with the more traditional measures of water quality. The implications of the findings are discussed.

A fibrescope was used to examine the internal condition of mains to determine if this could be related to consumer satisfaction and water quality. The findings are discussed.

The work undertaken indicates that the ALFI has an important contribution to make in the Water Industry. A revised model (Appendix A1.2) is to be manufactured for use in the Water Industry.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.