Water levels in many reservoirs and lakes have plummeted to less than half their capacity due to the region's driest start to the year since 1929. Seven million people will be hit. It is the first ban in the region since 1996.
Despite spells of rain over recent weeks, supply levels have failed to sufficiently increase and on Wednesday the company announced the "temporary" ban will come into force from 6am on Friday.
Anybody caught flouting the ban may face a fine of up to £1,000.
United Utilities water regulation manager John Sanders said: "Despite some recent rainfall in the north of the region, reservoir levels are still significantly lower than we would expect at this time of year and are now at a point where we need to impose some temporary restrictions on our customers.
"It is not a decision we have taken lightly, but a hosepipe can use as much water in an hour as a family of four would use in one day. This ban will help us to safeguard essential water supplies to our customers if the drought continues."
The ban will restrict the use of hosepipes or sprinklers for watering private gardens and washing private cars.
Customers have been told they can still water their gardens with a watering can and wash their vehicles using a bucket and sponge.
The Consumer Council for Water said it expects United Utilities to still "deliver a high quality customer service" and to be "particularly active on leakage". The group also promised to monitor United Utilities closely.