Jersey Water wants to turn Gigoulande Quarry in St Peter's Valley into a new reservoir to cope with future shortages.
The company has requested the new storage as part of a 'Water Strategy' that it's submitted for the Island Plan consultation.
Its Water Resources and Drought Management Plan, that's due to be published next year, predicts a shortfall of 8 million litres a day by 2045 between water demand and availability.
That's down mainly to the effects of climate change and growth in the population.
Other measures being considered are encouraging islanders to save water, more use of the desalination plant, extending the current reservoir and water recycling.
Jersey Water Chief Executive Helier Smith says action needs to be taken quickly.
"As an island with only 120 days of water storage when full, we are vulnerable to water shortages and drought. We need to begin work now to address the supply-demand deficit identified in our Water Resources Management Plan. It is important that the Island Plan recognises this strategic issue that will have multi-generational implications. The development of a Water Strategy within the Island Plan will help us ensure that Water Resources are considered alongside all of the other issues that need to be dealt with.
"The potential repurposing of Gigoulande Quarry as a water storage reservoir, represents a unique, once in a lifetime, opportunity to secure a key piece of infrastructure for the benefit of the island that, if ignored, will never present itself again. Filling the quarry with inert waste provides a temporary solution for solid waste management; filling the quarry with water provides a permanent water resource for the island for centuries to come."
The Gigoulande Quarry, which is currently earmarked for inert waste landfill, is estimated to have a capacity of around 30% (of existing water storage capacity), which is slightly less than the Val De La Mare reservoir.