The first occurred in unincorporated Contra Costa County, where a 6-inch cast iron main pipe burst just outside of Walnut Creek city limits at 1:15 a.m., according to East Bay utility spokeswoman Tracie Morales.
Morales said 43 customers are affected by that break.
The second break occurred within the city limits near the intersection of Walnut Boulevard and Ygnacio Valley Road and was reported at 2:46 a.m.
Morales said both water main breaks will be repaired by Saturday and are under investigation.