A hosepipe and sprinkler ban is to be imposed by Three Valleys Water to tackle the worst water shortages the South East has seen in a century.
Three million domestic customers will be affected by the ban
The firm's three million domestic customers in Essex, Beds, Bucks, Herts, North London and Middlesex will be hit by the ban, which begins on 3 April.
Last week Thames Water announced a hosepipe and sprinkler ban from April.
The companies are imposing restrictions after a prolonged period of below-average rainfall.
Andrew Marsh, of the Consumer Council for Water, said Three Valleys customers would find it easier to take a ban than homeowners in Thames Water areas as the company had a better track record on leakages.
"Customers will grumble about it, but they'll find it slightly easier to take," he said.
The South East has had two consecutive winters with below-average rainfall.
The period between November 2004 and January 2006 was the driest for more than 80 years, surpassing the drought of 1974-76.
The Environment Agency has warned that unless there is sufficient rainfall in the next few months, more drastic measures than a hosepipe and sprinkler ban may be needed.
It has not ruled out standpipes or supply cuts as a last resort.