Scilly Water Supply

There’s plenty of rainfall in the Isles of Scilly but much of it soaks into the ground leaving only a few small rivers.

Four of the five inhabited islands have freshwater ponds

and wells have been used to extract water from the ground.

However, the population of the islands is often massively increased by the arrival of tourists, particularly from mainland Britain and passing cruise ships.  At the peak of a dry summer up to 600 cubic metres of water per day can be needed.

This is obtained by a combination of extracting water from the ground via boreholes and purifying seawater via a desalination plant.

For desalination, seawater is taken into tanks, and then pumped across a membrane, which allows water molecules to pass through and returns salt and other impurities to the sea.

And here is where it happens, quietly and automatically, producing 400 cubic metres per day since the plant was opened in 2013.

The resulting water is cleaner than the water obtained from the ground, since the latter has high levels of nitrates from chemicals used in farming.

What actually comes out of the taps is a mixture of the two sources: the desalination water is mixed with the water from the boreholes so that the nitrates are diluted to well below the level deemed to be safe.