San Diego water customers will soon pay $6 to $13 more a month to fund the first part of the city’s new recycled water project, according to a newly released estimate.

The city is working on a multibillion-dollar plan to purify enough sewage to provide a third of the city’s drinking water by 2035.

Most of Southern California’s water now comes from either the rivers of Northern California or the Colorado River, which are not only hundreds of miles away but prone to drought. The city’s wastewater recycling project, known as Pure Water, is meant to provide more reliable water.

Of course, that will come at a cost.

There are numerous caveats to all the projections, but the takeaway is that rates will continue to climb in the short term. The San Diego region already has some of the highest water rates in the country, thanks in part to an expensive ocean water desalination plant that opened several years ago in Carlsbad.

Right now, the average San Diego customer pays $135 a month for water and wastewater service. Though, since bills are sent every two months, what customers have to pay at once is twice that.

Planning for the Pure Water project has already increased city bills by about $4 a month. By 2022, customers will be paying about $17 a month for Pure Water.

The number is particularly high that year because the city will be building the first, $1.4 billion phase of the project but it won’t be up and running yet. That means the city will have to continue to buy all the water it does now. It’s a bit like paying rent on an old apartment while you’re moving into a new one. As soon as Pure Water is up and running, that problem isn’t so bad. The city projects costs will begin to fall and hold steady at around $10 per month until the late 2040s.

By the mid-2050s, officials say Pure Water may save money because the recycled water could be cheaper than the water from the San Diego County Water Authority, which sells the city water imported from Northern California, Colorado and the Carlsbad desalination plant.

Charles Modica, the new deputy director of finance for the city water department, said over the next 40 years, customers will end up paying an average of $6 more a month, given current assumptions.

For years, city officials have declined to estimate publicly how much Pure Water will affect city water customers.

Officials prepared the analysis in response to repeated questions from Voice of San Diego.

“Pure Water is a major initiative of the mayor, a commitment that we’ve made to the ratepayers and to the citizens in terms of the longevity of making sure we have a long-term water supply going forward,” said Johnnie Perkins, the city’s deputy chief operating officer in charge of the water department.

In the long term, officials argue Pure Water may save ratepayers money and will certainly provide a more reliable supply of water.

Few, if any, customers are likely to see the exact increases described above. For one thing, the city is probably going to reconfigure its rate structure.

The city is also relying on a few assumptions that may not be true. Its estimates for how much it costs to generate recycled water are stale and haven’t been updated. It also expects San Diego County Water Authority prices to rise faster than that agency’s own estimates show.

The city’s new estimates also only cover the first part of the project, which is expected to generate 30 million gallons of drinkable water each day starting in 2023. Right now, the average San Diego water customer uses about 60 gallons of water per day and the state’s goal is to lower than number even further.

The second part of Pure Water will be even bigger and generate 53 million gallons per day of drinkable water. But serious planning for that project isn’t yet underway and any new facilities won’t be up and running for another decade and a half.

Back in 2015, the city expected it could do the entire multi-part project for about $3 billion in construction costs. Now, the city is looking to spend no less than $4.8 billion and perhaps as much as $9 billion.

Pure Water is ultimately an attempt to kill two birds with one stone. Not only will it provide a drought-proof source of water, but it helps with another long-standing city problem. For years, the city has promised to build Pure Water in order to avoid spending $2 billion to upgrade the Point Loma treatment plant, which dumps treated sewage into the ocean.

If Pure Water were only about treating sewage or only about getting a new water supply, it probably wouldn’t make financial sense. But, since it doesn’t make much sense to spend $2 billion on a plant that treats water that is dumped into the ocean, the city decided to spend more to treat the water so it is drinkable.