A Los Angeles city councilman is calling on the council and Mayor
The 38-member board is scheduled to vote Tuesday on whether to commit $4.3 billion in MWD funds to the project.
Echoing the concerns of some environmentalists that oppose the proposal, Koretz said ratepayer money should instead be spent on local water projects.
"It puts us on the hook for billions of dollars," Koretz, a former MWD board member, said of WaterFix.
Koretz's resolution is symbolic, since the city doesn't formally have a say in the proposal. However, his move could put pressure on the mayor.
Garcetti hasn't taken a position on WaterFix. Five of the MWD board members are appointed by the mayor.
WaterFix is a priority of Gov. Jerry Brown, who was in Southern California this week promoting the proposal.
Long planned, the project seeks to ease restrictions on water deliveries from the Sacramento-San Joaquin Delta. It involves the construction of new diversion points on the Sacramento River and two massive tunnels under the delta.
MWD imports water from the delta and sells it to Los Angeles and other Southern California water agencies serving 19 million people. The MWD staff has recommended that the board vote yes, saying the project is necessary to maintain deliveries of Northern California water.
Amid financial concerns, the Westlands Water District, the country's largest agriculture water district, voted last month not to participate in the plan.
Garcetti spokesman Alex Comisar declined to comment on Koretz's motion. Earlier in the week, he said the mayor is still considering the project.
"The mayor wants to protect ratepayers, develop local water resources, and ensure that L.A. has enough water for generations," Comisar said. "With that in mind, he is carefully looking at the project, listening to many opinions, and will decide based on the merits."
About two dozen activists protested outside Garcetti's home Wednesday night, calling on him to oppose the project.
Koretz said the city sought assurances from the MWD about WaterFix, such as requiring a public vote if the district's obligations changed. Those requests were "ignored," he said.
He said he hopes his resolution will be voted on at Tuesday's City Council meeting, before the MWD is expected to vote on the project that afternoon.
To go into effect, Koretz's resolution must be passed by the council and be approved by Garcetti, a spokesman for City Atty. Mike Feuer said Friday.