LONDON, July 17 (Xinhua) -- Millions of households in the northwest of England will face a hosepipe ban as the longest heatwave in more than 40 years continues in Britain, said a major water company Tuesday.

The water supplier United Utilities said a total of 7 million customers would be affected by the first hosepipe ban since 2012, which is due to come into force on Aug. 5.

Martin Padley, the company's water services director, said despite some recent rainfall, reservoir levels are still lower than expected at this time of year.

"With forecasters predicting a return to hot dry weather for the rest of July, we are now at a point where we will need to impose some temporary restrictions on customers," Padley said.

It is reported that in the northwest of England, reservoir levels now are 17 percent lower than the same period last year. The water company is already having to move water around the region to maintain supplies.

In the northwest part of England, water supply relies heavily on open water sources like reservoirs, rather than large reserves of ground water from boreholes.

A hosepipe ban can reduce water usage by 5 to 10 percent, according to UK Water Industry Research.

In Northern Ireland, a hosepipe ban has been in effect since June 29, with an extra 175 million litres of water being pumped into the network in an effort to keep up with demand.

Met Office said that there was no significant rainfall expected in the northwest of England during the next week.

Water companies around the country are all asking customers to use water wisely in the garden and avoid washing cars and windows until it begins to cool down.

United Utilities, which operates in the northwest of England, has urged people to save water by turning off garden sprinklers, not using hosepipes, not washing cars and taking shorter showers.