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.