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 May 23:

* ANC 6B (work area bounded by E Street SE, Seventh Street SE, G Street SE and Fourth Street SE).

* ANC 3D (work area bounded by Lowell Street NW, New Mexico Avenue NW, Fulton Street NW and 49th Street NW).

* ANC 3G (work area bounded by Western Avenue, 32nd Street NW, Morrison Street NW, Broad Branch Road NW).

* ANC 5B (work area bounded by Rhode Island Avenue NW, Bryant Street NW, New York Avenue NW and Fifth Street NE).

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,