Main Cleaning

2023 Water Main Cleaning Program

The Alameda County Water District (ACWD) is scheduled to clean all dead-end mains in Fremont, Newark, and Union City to improve water quality and remove sediment buildup in pipes that may cause discolored water. This is part of the vital service provided by ACWD to ensure that all customers receive high quality water.

To align with the District’s Water Shortage Contingency Plan, the 2023 Main Cleaning Program is modified to support ACWD’s water conservation efforts. This modification will allow us to save approximately 50% of the water which is typically used for the Main Cleaning Program and will help us meet the water use reduction goals outlined in the adopted ACWD Water Shortage Emergency and Mandatory Restrictions on Water Use Ordinance. Although fewer mains will be cleaned in 2023, ACWD strives to meet all regulatory requirements and maintain system performance.

Cleaning will occur from the end of January 2023 through April 2023; Monday through Friday, 7 a.m. to 4 p.m. (excluding holidays). The program schedule and updates will be posted to this webpage in January 2023.

How the Main Cleaning Program Works


ACWD cleans water mains to remove the buildup in pipes that may cause discolored water. This is accomplished by opening fire hydrants. As the water flows at high velocities through the mains, scale and fine sediment are dislodged. The resulting discolored water leaves the distribution system through the open fire hydrants. Since some of this water eventually flows into San Francisco Bay, ACWD utilizes disinfectant and sediment removal best management practices to minimize impacts to the environment.

Main cleaning may result in a brief period of discolored tap water for some Tri-City residents from January-June. Despite its appearance, the water will remain safe for household uses such as drinking and cooking. You should, however, minimize water use and avoid washing light-colored laundry from 7:00 a.m. to 4:00 p.m. on the day or week main cleaning is scheduled for your neighborhood.

Evaluation of Recapture Options

Prior to resuming the main cleaning program this year, ACWD staff thoroughly examined possible recapture methods for the main cleaning discharges and will continue to do so. As much as ACWD would like to be able to reuse water from the main cleaning program, unfortunately, in most cases, it's just not technically feasible. In order to clean our mains and continue to ensure high quality water for our customers, we need to flush at very high  flow rates that are not possible to recapture. The amount of trucks, transit time for the trucks, gas, etc. needed to recapture the water would be excessive. Directing the water to a truck would be very time-consuming and resource intensive, significantly increasing costs of the State-required processes.