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I’m working on a large water supply network. I’d like to set up a proper water quality plan to monitor and protect the water quality. Which parameters should I monitor, where and when?

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A conventional ‘quality control’ approach involves testing water from the source to the point of use.

In addition to this approach, your water quality plan – also called ‘Water Safety Plan’ – should also identify the possible risks (i.e. critical control points where water could be contaminated) and the actions to prevent and limit these risks. This plan will help you to evaluate if your water quality plan is efficient.

Many organizations and institutions are implementing Water Safety Plans, which is a quality assurance approach to water safety, protecting water from the point of source to the point of use, and using water quality testing as a tool to make sure that the Water Safety Plan is working. Have a look to the WEDC briefing note on Water Safety Plan: https://wedc-knowledge.lboro.ac.uk/re...

Parameters

Many water quality standards are based in the WHO guidelines. But each country would have his own regulation and surveillance bodies. In addition, function of the context where you’re working and the risks of water contamination you might exposed to (i.e. industrial and agricultural pollutions), some additional parameters should be considered. However, keep in mind that reducing bacterial contaminants is always the priority because of its direct impact on health. For instance, a long time exposure to chemical contamination is necessary before health effects manifest themselves.

If risks of chemical contamination have been identified, specific measures should be taken (i.e. select a new water source, set up a specific water treatment).

The key parameters to be monitored would be the following ones:

• Microbiological: faecal coliforms indicating risks of faecal contamination, having direct impact on health.

• Chemical:

o Nitrate, arsenic and fluoride: according to WHO, chemical of primary concern with high health risks, consumption of nitrate leading to blue baby syndrome, arsenic to arsenicosis and fluoride to fluorosis;

o Iron: no health-based guideline values, but could concern the users regarding the water colour, odour and taste;

• Physico-chemical

o pH: influence the treatment effectiveness;

o Turbidity: good indicator to determine which treatment to be set up and also to monitor the treatment efficiency;

o Total dissolved solids;

o Temperature: indicator of pollution and impact on treatment;

o Chlorine residual: to make sure that the levels of chlorine remaining after treatment are high enough to prevent any opportunistic contamination.

Sampling

On your large water supply network, you need to establish the following sampling points:

• At the outlet of the water source;

• At the outlet of the treatment plant;

• At the outlet of the storage tank;

• Within the distribution system, close and far to the point the water enters the distribution system (main lines, remote branches, dead-ends and household connections).

Frequency of sampling

As explained above, your water quality testing should be complementary of your water safety plan. The identification of risks and possible point of contamination may influence your frequency of sampling. Thus, for your large water supply network, the water quality testing could be done once a year, or less if there is ... (plus)

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