Search Contact Menu
24 hour - 01481 239500

Other useful numbers

News Centre > Friday 21 July 2017

Water treatment strategy review 2017

Juas WTW

A new water treatment strategy aims to save Guernsey Water customers £10 million over the next 25 years. 

The new plan follows a comprehensive review of the island's existing and future provisions.  It will see the closure of one treatment works and the recommissioning of another, which will significantly reduce electricity consumption, chemical use and costs. 

Of the three existing water treatment works (WTWs), St Saviour's and Kings Mills will be retained but Longue Hougue will close.  In its place, the former works at Juas Quarry, in Vale, will be brought back into operation, with the addition of a new ultraviolet sterilisation system. 

The three WTWs will be able to meet peak consumption demand, even allowing for planned or emergency shutdowns.

Along with St Saviour's, Longue Hougue is one of two existing treatment works to use "membrane technology".  Although the former will be retained, the longer term focus will be on more traditional filtration methods. 

Guernsey Water's general manager, Stephen Langlois said closing Longue Hougue and recommissioning Juas will significantly improve operational efficiency and provide a more reliable, better quality drinking water supply.This will be better value for customers. 

"There is little variation in the quality of drinking water produced at each of our treatment works, but the conventional methods at Kings Mills and historically at Juas are substantially more efficient than our membrane filters.  This is mainly because our membrane filters use around three times more power and 50% more chemicals than our conventional treatment processes.

"Adding to this, the filters at St Saviours and Longue Hougue also need to be replaced every 10 years, at a cost of more than £1m each time.

"The frequency of regular membrane cleaning at Longue Hougue has started to increase, which means we must begin planning for their replacement. This added to other process issues at Longue Hougue means substantial investment is needed at the site.

"Rather than simply continue to invest in Longue Hougue, two years ago we took a step back and developed a strategy for all our water treatment works. This concluded that, in the long term, investing £1.8 million in bringing Juas back online would give customers substantially better value for money. We expect that overall this will save around £200,000 per year and around £10 million over the next 25 years.

"Efficiency is one of the three main themes in our business plan. With many other cost pressures all areas of the business, including water treatment, must be efficient; this helps to constrain bill increases for customers.

"The other two themes of service and strategy are also well supported by the strategy; the refurbishment of Juas will improve drinking water quality through the provision of ultra violet disinfection and give us the option of carbon dosing, to deal with any seasonal taste issues. Both are tried and tested water treatment techniques.

"Strategically Juas is also more resilient as, unlike Longue Hougue, it can treat water from more than one source. This means that if the water quality of one source deteriorates we can switch to another," he said.


The utility is planning for Juas to be operational by the summer of 2018. The phased closure of Longue Hougue will start shortly afterwards.

Responsibility to our customers and the environment

View Our 6 Outcomes
Have a question or cannot find what you are looking for? Try our support pages. Go
Happy to help