Longue Hougue reservoir essential to island's long term water supply

Following several requests for information regarding the current and future use of Longue Hougue reservoir, Guernsey Water is emphasising its critical importance for the future of the island's water supply.

Ahead of the publication later this year of Guernsey Water's Water Resources and Drought Management Plan, Steve Langlois, general manager of Guernsey Water, revealed that the plan considers long term water supply and demand.  It also takes into account many factors that may impact the island's water supplies over the next 25 years, such as population changes and the impact of climate change on water collection, storage and use.

"The need to have adequate water resources is of critical importance to Guernsey's future.  While the current level of protection from drought is comparable to other water companies in the south of England, our long term needs and our future supplies are finely balanced," said Mr Langlois.

Longue Hougue is the largest reservoir on the island with a capacity of 1.16m cubic metres and provides water for islanders every day.  It contributes more than 26% of Guernsey's total water resources. Some people believe that our water supply could be affected by sea water getting into the reservoir, but we have absolutely no evidence to suggest that this is the case. We have tested the chloride (salt) levels in Longue Hougue reservoir weekly since 2009, and there is negligible difference between the levels here and those in our other main reservoirs such as St Saviours.

Guernsey Water says that Longue Hougue is a vital component of the island's "finely balanced" water supply.   "Any change in the use of Longue Hougue reservoir without introducing an alternative would leave Guernsey at unacceptable risk of drought," he said.

Questions have been raised about whether Longue Hougue reservoir can be used for the disposal of inert waste, but no viable alternative options to the existing reservoir could be brought online by 2022, when a new solution for inert waste would be required. 

"The timeframe of the current inert waste strategy is considerably shorter than would be needed to replace Longue Hougue reservoir with an alternative, such as Les Vardes quarry," said Mr Langlois.

"Converting Les Vardes quarry into a reservoir would be totally unfeasible within this period, mainly because it is expected to remain in operation by Ronez well beyond the timeframe being considered. It would also require major investment over a substantial period of time. There is no existing network of raw water pipes close by, and those nearest are smaller than would be needed to fill the reservoir and transfer water to our water treatment works.  During this timeframe it is simply not a viable option," said Mr Langlois.

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