San Diego’s water rates will climb nearly 15 percent during the next two years, after the City Council voted overwhelmingly for the hike Thursday.

“No one likes water rate increases, but this increase is a prudent and necessary step,” Interim Mayor Todd Gloria said before the council voted 8-1. Councilman Scott Sherman opposed the measure, which will take effect Jan. 1.

City officials said the higher rates will ensure that San Diego has the financial reserves needed to maintain its good bond rating and cover rising wholesale water costs.

“This rate increase is actually compounded by the fact that we did not raise rates for two years,” said Vincent Mudd, a San Diego representative on the San Diego County Water Authority board.

The average increase of 15 percent won’t be felt equally.

Under a new pricing structure, single-family households with very low water use will see their rates rise about 8 percent over the next two years. In contrast, homeowners consuming the most water will see rates double.

In a significant change, each new pricing tier will be based on less water usage than under the current system. That means more people will be bumped into higher pricing levels.

Rates for multi-family dwellings and nonresidential users will jump nearly 20 percent by 2015, and construction and irrigation users will see hikes of almost 24 percent by the second year.

Some labor advocates, business owners and residents came to Thursday’s council meeting to voice their criticism of the rate proposal. They said it would hurt the poorest San Diegans and unfairly punish certain single-family homeowners with sharply higher rates.

Several homeowners said although they’ve taken steps to conserve water, they’re still in the highest price bracket.

“The fact that you’re changing the tier structure and going up 100 percent, it’s going to affect families the most,” said Chris Rizzuti of Rancho Bernardo. “It’s an attempt to push an agenda of water conservation that does not take into account multiple people in a household.”

Sherman said he shared that concern.

“I have a real problem with the rate tiers,” Sherman said. “It puts us on this council of being in the position of choosing winners and losers.”

But water officials and supporters of the change said the higher rates are needed.

Cesar Rios of Mission Hills, who said his family’s water use is in the lowest tier, said the significant increase for the highest usage bracket rightly should encourage conservation.

“I don’t think it’s going up enough,” he said. “The cheapest gallon of water is the one you don’t use.”

The rate hike follows years of sharp increases for the City of San Diego and the region at large, as the cost of imported water swelled and supplies from the Bay Delta and Colorado River became less reliable.

Over the years, Los Angeles-based Metropolitan Water District, which provides nearly half the water used in San Diego County, raised the rates it charges to the San Diego County Water Authority, the region’s wholesaler. The water authority then boosted its own charges to individual water agencies, including the San Diego Public Utilities Department.

Wholesale water rates soared between 7.5 percent and 15.4 percent for untreated water and 7.7 percent to 18.1 percent for treated water during each of the past five years, according to the water authority.

Although San Diego avoided passing on those costs to its customers in 2012 and 2013 by drawing more water from its reservoirs, trimming operational costs and refinancing bonds, officials said they could no longer keep rates down.

In May, the water authority announced that it would limit its rate increases for member agencies to 2.6 percent for untreated water and 3.5 percent for treated water in 2014. But San Diego decided to impose steeper rate hikes for its customers to cover prior years that had no price increases, as well as anticipated increases for the next two years.

The council vote also restructured water pricing for single family homes. In place of the existing three tier structure, it splits single family bills into four tiers, adding an ultra-low water use category at the bottom.

Users in that category, which ranges from zero to four hundred cubic feet per month, should see less change in their water bills, since a slight reduction in the monthly base fee will balance out small increases in water rates at the lowest level.

Customers using 400 cubic feet per month, for instance, will see their bills go from about $34 in 2013 to $36 in 2015, according to a city report showing sample residential water bills.

Customers in the middle tiers will see increases of a few dollars per month as a result of the rate hikes, the report showed. Over 20 percent of the city’s customers fall into the first tier, and another 50 percent fall into the second category, said J. Brent Eidson, a spokesman for the City of San Diego Public Utilities Department.

But residential customers using more than 1,900 cubic feet per month will see sharp spikes in the cost of those extra gallons. They make up about 10 percent of the water city’s customers, officials said.

Water rates will double in the highest tier, from the current rate of $4.40 per hundred cubic feet to $8.80 in 2015. That increase wouldn’t apply to the entire bill, but only to water use over 1,900 feet per month. So a residential customer using 2,500 cubic feet per month would see monthly bills swell from about $120 to $170.