United Utilities sent the message via email and reassured customers that it was “unlikely to be harmful”.
But the company advised that water should not be given to bottle-fed children until clear.
The message said: “You may notice your water is discoloured or brown in colour.
“This is unlikely to be harmful and can be cleared by running your first cold tap slowly.
“Please avoid doing any clothes washing and do not give the water to bottled fed children until clear.
“Sorry for any inconvenience.”
The company advises that more information on discoloured water can be found at www.unitedutilities.com.