A hosepipe ban could be on the way due to three years of drought conditions.
Affinity Water, which supplies water to homes across Essex, has warned customers it "may need to introduce water restrictions in spring 2020".
In a letter to more than 3.6m customers the firm's chief executive Pauline Walsh explained there had been less rain than usual in recent years meaning drastic action may need to be taken.
While the letter arrived as most of the country was being lashed by torrential downpours its message was clear - there is simply not enough water.
MORE: Suffolk could lose Sainsbury's and Argos stores as 125 closures revealedMs Walsh wrote: "Despite today's wet weather it may come as a surprise that over the last three years we've had much less rain than normal.
"This means we are now in drought and we may need to introduce water restrictions (also known as a hosepipe ban) in spring 2020.
"We rely on rain, especially in winter, to supply your water. The rain this week is not enough to make up for three years of dry weather.
"There's lots we're doing but you can help too."
Affinity supplies water to the Tendring district of Essex, including Clacton-on-Sea, Manningtree, Frinton-on Sea and Harwich.
As well as serving parts of Bedfordshire, Berkshire, Buckinghamshire, Essex, Hertfordshire, Surrey, and London.
The letter says customers would make a "real difference" by saving a bucket of water a day by, for example, reducing the length of showers by a minute or taking advantage of the rain and using a water butt for gardening.
Ms Walsh added: "We hope we can all work together to save water during this time, and we will be updating you throughout the autumn and winter.
"In the meantime, if you are affected by the heavy rain and you have concerns please visit the Environment Agency's website."
The letter follows recent figures from the Consumer Council for Water (CCWater) showing that Affinity failed its leakage target for a second successive year in 2018/19.
The company lost an average of 130 litres of water per property per day, making it the fourth worst performer across England and Wales.
Dr Mike Keil, head of policy and research at CCWater, said: "Customers can help to reduce the risk of restrictions next spring by using water as wisely as they can, but we also expect Affinity Water to be doing everything in its power to manage its resources effectively, including boosting its efforts to tackle leakage.
"Affinity has failed its leakage target the past two years and that doesn't send the right message to customers at a time when all of us need to play our part in protecting our water resources from the demands of climate change and population growth."
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