The water situation on St Mary's could become a crisis if islanders do not do as much as they can to conserve the supply.
Cllr Steve Sims, Lead Member for Place, said that the island may lose ground-sourced water for a generation if levels become low enough for saltwater to contaminate the water table.
He also said that the pool and other non-essential services may have to close if the situation continues.
He told Radio Scilly: "We have a critical water situation at the moment on St Mary's and Bryher. Bryher is slightly worse off than St Mary's but as the off-islands always do, they have pulled together and have decreased their consumption by a significant amount. They're certainly not out of the woods but they have reduced their consumption, which is what we have to do on St Mary's.
"If you can save water, please do so any way you can. I know Hugh Town looks lovely at the moment with all the hanging baskets but if you can water them with old washing-up water, plants don't care. Don't use tap water for it. If you can bear the stink, or the rest of the family can, have a shower on alternate days rather than every day. Don't go thirsty, drinking isn't an issue.
"I don't think we have the powers to ban sprinklers and hosepipes... but really it's a matter of good faith. What you should do is not use hosepipes, not wash the car. Have it as a badge of honour for a few weeks having a dirty car. Use the eco setting on your washing machine."
He went on to explain the dangers of saline intrusion, saying; "A lot of the water is under Porth Hellick and we have big spring tides in the middle of August. If the water level is too low you can get saline intrusion, where the salt water goes into the water table and contaminates the fresh water that floats on top. If that happens it takes 40 odd years to settle. Then we really are stuffed for a generation because we won't have any water on St Mary's unless we use the desalination plant, which is hugely expensive."
The Council has enough bottles of water stored for all the islands for a day and can import water in tankers from the mainland in the short term if necessary. However, weeks of wet weather are now required to fully replenish the water supply and the dry period is forecast to continue through August.
Cllr Sims added: "We are looking at upgrading the desalination plant. The issue is we can't get enough power down to the pumps. It's working at full tilt at the moment all the time, and that's another issue - if you work something at 100% it wears out quickly. If you want proper efficiency, you want it running at 60-70%.
"We are now looking at shutting down non-essential services. The public showers have been shut down, we have to consider whether to shut the pool down for the interim. It's really, really important that everyone do what they can to conserve water. If people think before they turn the tap on or flush the toilet and actually use water sensibly, it should be fine."
The Council published a notice on July 17th warning that the water supply on St Mary's and Bryher is now "critically low".