Environment Agency chief executive Philip Duffy said: “Record-breaking summer heat and severe drought have put our water resources under immense pressure.
“Recovery depends on both rainfall and how much water we use. We cannot change the weather, but water companies can act now.
“We expect them to follow their drought plans and take the steps needed to secure public water supplies.
“We are also asking everyone to use less water. That will leave more in our rivers and the environment, helping farmers and protecting wildlife and nature.”
The government said the South East and South West had experienced their driest April to September in more than a century, impacting reservoir levels in that area.
Environment Secretary Dame Angela Eagle said: “This level of drought is something we have not experienced for decades, so this government is stepping up our support and planning.
“We are working closely with water companies to protect public supplies in the areas affected, and I’d continue to urge everyone to think about how they can use water wisely over the coming weeks.”