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Water usage on St Mary's 'unsustainable'

The Council of the Isles of Scilly has issued a further warning about the worsening water shortage on St Mary's.

In a notice published on Monday July 30th, Senior Manager for Infrastructure Craig Dryden said that islanders need to take significant steps to reduce their consumption "before it is too late".

The notice reads:

Water usage has reached an unsustainable level on St Mary’s and the Council is unable to meet demand without seriously damaging our wells and boreholes. The extreme dry period this summer is set to continue so we must ask all of our customers to take significant steps to decrease their water usage before it is too late. Please read and share this notice.

Desalination isn’t enough

Contrary to what you may have heard, the desalination plant cannot meet all our water needs alone. The plant only provides around a third of demand.

Furthermore, running the equipment at maximum rate, as we are now doing, greatly increases the risk of a breakdown. There is no backup desalination plant.

Groundwater depletion

Most of our supply comes from groundwater. This is the subsurface water accessed by drilling boreholes into the granite bedrock. Unlike surface reservoirs, these sources are extremely difficult to monitor. However, all of our tests indicate that the groundwater supply is at an historic low and is being extracted at an unsustainable rate. This creates three problems:

  1. - We may run out of groundwater.

  2. - The groundwater contaminant concentration may become too high to be treated.

  3. - The low pressure and reduced levels in the groundwater could result in seawater getting into the wells and boreholes and contaminating the water, causing the source to be unusable for a generation.

We need to reduce our reliance on groundwater by decreasing our water consumption.

What about the reservoirs?

There are no reservoirs on the Isles of Scilly. St Mary’s has 3 water tanks that continually fill with drinking water. They replenish at night when usage is low but are often empty by the end of each day.

What happens if we run out of water?

The Council has emergency plans in place should the islands run out of water. In short, this would involve shipping water to the islands with a ration per head each day. Clearly we need to avoid this situation.


When our crews attend a fire on St Mary’s, they are generally reliant on drinking water to put out the blaze. As we don’t have a reservoir, a single fire can greatly diminish our daily supply of water. Please do what you can to reduce the risk of fire:

- Do not light a bonfire for any reason.

- Do not use fire as part of any farming activities.

- If you are having a barbecue, take all possible measures to ensure you do not cause a fire.

- Make sure you reduce the risk of fire in your house and outbuildings. Our fire service can help (see details at the end of this notice).

If you would like advice on fire prevention don’t hesitate to contact us at 01720 424403 or

Should I reduce the amount of water I drink?

Just so there is no confusion, you should continue to stay hydrated in the hot weather and drink as much water as you need. We would never ask people to restrict the amount of water they drink. We do ask that you don’t waste water by running the tap until it runs cold and that you keep your water usage to a minimum when washing.

Are you implementing a hosepipe ban?

Not formally. We are asking all of our customers to please cease any use of hosepipes, sprinklers and paddling pools and to keep other water usage to an absolute minimum.

It is actually unclear whether the Council can impose a ban under current legislation. In any case, we don’t want to fine anybody, we just want everyone to respect the needs of the wider community and to not use hosepipes or sprinklers during this critical summertime period.

Report leaks no matter where you find them

Amazingly, a single dripping tap can waste over 5,000 litres of water a year and could fill a paddling pool every week. If you’re unsure about a leak, please don’t hesitate to contact us at 01720 424403 or

You should also report leaks if you find them at other premises; speak to the owner of the property or business.

Thank you for your cooperation.


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