Water restrictions have been extended until at least Tuesday for 1.8 million residents in Montgomery and Prince George's counties, an unwelcome development for homeowners -- and their browning lawns -- sweating in expected 100-degree heat for the next few days.

The Washington Suburban Sanitary Commission, the water agency for the two counties, replaced the damaged portion of an 8-foot Potomac water main that nearly burst last week. But officials said they weren't able to finish water-quality testing, which takes at least 18 hours to complete.

"Our actions over the last five days have been with the best interest of the public in mind, and it is best now to continue the restrictions," said WSSC General Manager Jerry N. Johnson. "We regret the inconvenience, but we thank you for cooperation so far, and we need that cooperation to continue."

The agency banned outdoor water use in an effort to secure water pressure and told customers to turn on their indoor faucets only when necessary.

Though compliance has increased, many are still watering lawns, washing cars and flushing toilets at the same pace.

WSSC police issued about 300 warnings by Monday evening, and four people were given $500 fines for repeat violations. Water use fell by roughly 14 percent, less than half of the agency's 30 percent goal.

Who you gonna call? ยป  To report water violations, dial 311 in Montgomery County or the WSSC hotline at (301) 206-8888.

Washingtonians might not want to go outside anyway. The Metropolitan Washington Council of Governments issued a Code Red warning, unhealthy air for everyone, that runs through Wednesday. Even with the underwhelming response, agency officials say restrictions will be lifted after testing is completed. They were aided by a relatively uneventful holiday weekend, avoiding massive fires that could have challenged water pressure levels.

The damaged 96-inch main near Tuckerman Lane and Gainsborough Road, the largest pipe in the network, was identified by fiber-optic technology being implemented throughout WSSC's system of 5,500 miles of freshwater pipes and nearly 5,400 miles of sewer pipeline.

However, water networks throughout the region are routinely cited as outdated.

Nearly a quarter of all WSSC pipes are at least a half-century old, and there were 1,534 water main breaks or leaks in 2009, according to the most recent data. Virginia and District water pipes are an average of 80 years old.