Effective QA implementation – Chlorine monitoring & network flushing a priority


Feargal Hughes of Glaslough/Tyholland GWS takes a water sample from one of several dedicated sampling kiosks installed on the distribution network.

While the recent National Federation of Group Water Schemes (NFGWS) Rural Water Webinar focused on future-proofing the rural water sector, Dr Michelle Minihan reminded us that microbiological contamination remains the single great threat to the safety of drinking water supplies.

Addressing emerging contaminants in the sector, the head of the Environmental Protection Agency’s (EPA) Drinking Water Inspectorate informed delegates that the proper functioning of disinfection systems and quality assurance implementation on networks should always be a priority for schemes.

Responding to this message, NFGWS development officers have begun a new phase of Quality Assurance site visits to group water schemes that focuses primarily on chlorine monitoring and on the need for periodic flushing of the distribution network.

The focus on chlorination is especially important in an Irish context given the scale of faecal contamination in raw water sources, with VTEC E.coli levels 9 times higher than in other European countries.

Disinfection procedures demand verification and those schemes that don’t, as yet, have professional management of their treatment plants must be confident that dosing systems are working as they should be and that there is an automatic shutdown of the supply should they fail, while all schemes need to maintain records of chlorine levels in the pipework.

The benefit of chlorination is that it continues to protect water in the distribution network from contamination due to breaks in pipework, back-siphoning etc. For this reason, it is imperative that schemes are monitoring chlorine levels in their pipework, measuring both total and ‘free’ chlorine levels, establishing trends and interpreting results.


While the EPA insists on a minimum 0.1mg/l at the end of the network, the NFGWS is asking schemes to aim for higher. It is further suggesting that small schemes take at least one chlorine sample each day, while larger schemes should be ensuring that every leg of the scheme is sampled at least once weekly.

Boards are encouraged to investigate the possibility of assigning the task to interested members on each branch of the network. Beyond taking samples, the Federation is reiterating the importance of ensuring that chlorine monitors are calibrated and that the results are recorded on the appropriate template sheets.

To drive home these messages, the Federation will shortly launch a training video for schemes on the proper procedure for sampling and recording chlorine levels in the network.

Line flushing

A further training video is under preparation to demonstrate the correct procedure for flushing distribution mains.

All schemes, whether sourcing their water from a borehole, spring or surface water body, need to flush their entire network from time to time, while schemes on impacted lakes should be aiming to flush more regularly, with the frequency determined by chlorine and turbidity monitoring results.

This is important because natural substances, such as manganese, will settle in the pipework over time, making it more and more difficult to maintain a chlorine residual. Indeed, recent research suggests that manganese levels as low as 17ug/l will result in carry over into the network.


As with chlorine monitoring, it is critical that proper records are maintained of line flushing, not least because Water Services Authorities will require documentary evidence of proper management of a GWS supply in the course of conducting an audit.

This article originally featured in the autumn edition of the Rural Water News magazine. To read the full edition and to sign up to our magazine mailing list, click here.