The D.C. Water and Sewer Authority (WASA) has begun an annual program to flush water mains throughout the city, a procedure designed to remove sediments and improve drinking water quality.

Each week, from 10 p.m. to 6:30 a.m. Sunday through Thursday, WASA crews will open fire hydrants in designated neighborhoods and flush water.

The water supply to customers will not be shut off during the flushing.

Customers might notice some water discoloration in the early morning hours. If that happens, WASA recommends that residents open the cold water tap and allow the water to flow slowly until the water is clear.

Customers should not run hot water or do laundry during the flushing. If the hot water becomes discolored, WASA recommends flushing the hot water tank by opening the valve at the bottom of the tank.

The flushing program will continue through November.

These neighborhoods, with boundary streets, are scheduled for flushing the week beginning July 11:

* ANC 6B (work area in Northeast, bounded by F Street, 17th Street, Constitution Avenue and 13th Street).

* ANC 4C (work area in Northwest, bounded by Allison Street, Rock Creek Church Road, Upshur Street, and Illinois Avenue).

* ANC 2B (work area in Northwest, bounded by O Street, 26th Street, M Street and 29th Street).

* ANC 5A (work area in Northeast, bounded by V Street, South Dakota Avenue, R Street and Bladensburg Road).

For information, call the WASA Water Quality Office, 202-612-3440, 8 a.m. to

4 p.m. In an emergency, call WASA's 24-hour hotline,