A new analysis says water rates in San Diego must go up another 44.2% between 2028 and 2031 even though the City Council agreed in October to raise them a cumulative 31.3% this year and next.

If the council ends up approving additional hikes that large when they come to a vote next year, the cumulative six-year rate increase would amount to more than 90%.

The 54-page analysis, which was presented to the council Monday, also says sewer rates must rise a total of 15% in 2030 and 2031. Those increases would be on top of an already-approved four-year cumulative hike of 31%.

Council members and other city leaders vowed Monday to spend the next 12 to 18 months searching for ways to boost revenue or cut spending for the city’s water and sewer systems that could prevent such large hikes.

But the city’s independent budget analyst and the council’s leading voice on water issues said making a serious dent in those increases will be a major challenge.

“Unless there are significant expenditure or revenue assumption changes that happen in the next year, this outlook and the rates included in it are the rates that the council will be asked to approve,” said Jordan More of the IBA.

More said the new analysis, called a five-year outlook, shows that city water and sewer officials have already found and implemented the lion’s share of possible cost-saving innovations and revenue enhancements.

“This really does show that the system is under financial strain and that the rate increases are needed unless other changes are made,” More said of the outlook.

The city has limited leverage because it essentially must pass on to its ratepayers any increases to what the city must pay the county water authority for imported water.

And the water authority is projecting steep rate increases in the coming years that are responsible for about two-thirds of the city water rate hikes called for in the new analysis.

The water authority is contractually obligated to buy more water than its member agencies typically need, forcing it to raise rates to cover its built-in costs.

The outlook is projecting such large rate hikes despite the city’s decision to delay dozens of key infrastructure projects by three years to reduce expenses.

Officials had planned last summer to postpone many projects by two years, but they extended that to three years after the council refused to approve four-year water rate hikes and opted for two-year hikes instead.

“We can’t put anything into construction without having a full knowledge of what our upcoming rate increases would be,” said Lisa Celaya, the city’s executive assistant director of public utilities.

The change boosted the number of delayed projects from 138 to 190.

More said there could be significant consequences to delaying infrastructure projects, which city officials refer to by the insider acronym CIP for “capital improvement program.”

“If you keep deferring CIP projects to delay a rate increase, those CIP projects are going to run into some other big projects that are on the horizon and your capacity to do all that stuff at once is going to be extremely limited,” More said.

Councilmember Henry Foster suggested the council take a detailed look at personnel and operating costs in the water and sewer systems.

Khota Zaiser, an aide to Mayor Todd Gloria, said the upcoming budget season could be a good time for that.

“The next few months — the budget development process — will allow us to lift the hood and see what other pathways are possible,” Zaiser said.

Councilmember Sean Elo-Rivera reiterated his desire for the city’s water and sewer systems to maximize revenue from dozens of properties they lease out.

Celaya said city officials are analyzing those leases, which total about $7 million in annual revenue before any negotiations on increases.

Councilmember Stephen Whitburn said searching for efficiencies is worthwhile and admirable but also stressed that the size of the problem is gigantic and that water costs are the key driver.

“The efficiencies, as necessary as they are, pale in comparison with the cost of the water,” said Whitburn, who represents the council on the county water authority board. “The cost of the water is far and away where the money is in this conversation.”

The outlook calls for increases of 11.5% in 2028, 11% in 2029, 11% in 2030 and 5% in 2031. Those would come on top of hikes of 14.7% on Jan. 1 and 14.5% scheduled for January 2027.

In addition to ratepayers in the city of San Diego, the projected water rate increases would affect customers in Coronado, Imperial Beach and Del Mar who are part of San Diego’s water system.

The outlook calls for sewer hikes of 8% in 2030 and 7% in 2031. Cumulative hikes of 31% in 2026, 2027, 2028 and 2029 have already been approved.

The sewer increases would go beyond San Diego and also affect ratepayers in Chula Vista, El Cajon, La Mesa, Lemon Grove, National City, Coronado, Imperial Beach, Del Mar, Santee, Poway and some parts of the South Bay and unincorporated areas.