Water bills in San Francisco are set to rise steadily over the next four years, after the approval of a rate schedule by the city’s Public Utilities Commission.

The city’s combined bill for water and sewer services will climb by an average of 8.4 percent, or around $10, each year through 2022, according to the commission.

The agency settled on when and how much rates would rise after a 1½-year study partly tied to the city’s budgeting process and schedules set by the City Charter.

Water and sewer rates across San Francisco will go up by 7.4 percent starting July 1.

Bills for households currently paying $108 per month — the citywide average for single-family homes — will increase by $8. That number will grow to $126 in 2020, $137 in 2021 and $149 in 2022.

The commission has pegged the average monthly water use for single-family dwellings at about 3,964 gallons.

In addition to funding the commission’s regular operations, the rate increases will pay for a series of ambitious infrastructure upgrades to the city’s sewer system and vast Hetch Hetchy network that sends drinking water to 2.7 million Bay Area residents.

Most of the upgrades are designed to make the city’s water and sewer systems more efficient, more responsive to sea level rise and other effects of climate change, and better equipped to withstand earthquakes.

Eric Sandler, the commission’s chief financial officer and assistant general manager, said the most significant project is the agency’s Water System Improvement Program, $4.8 billion in upgrades consisting of 83 projects.

At $810 million, the largest of those projects is the construction of a new Calaveras Dam in the hills of the Sunol Valley. The earthen dam sits just 1,500 feet from the Calaveras Fault, which is capable of producing a 7.25-magnitude earthquake. The new dam, which is nearing completion, is being constructed to withstand a temblor of that magnitude.

The commission is also moving ahead with its Sewer System Improvement Program, which will be rolled out in phases through 2032. The city’s sewer system, which is more than 100 years old in some places, is ill-equipped to handle the rising sea-levels associated with climate change and the infrastructure strains accompanying San Francisco’s surging population.

Last month, the commission approved a $1.3 billion upgrade to the solid-waste processing facilities at the city’s Southeast Treatment Plant, which processes 80 percent of the city’s wastewater. The upgrades are intended to make solid wastewater treatment more efficient and reduce the offensive odors generated by the sewage plant.

While rising monthly water bills in an already expensive city can be tough to stomach, Sandler said the commission’s projects are essential to ensuring San Francisco has a reliable and resilient water system.

“The interesting thing about our infrastructure in particular is that you don’t see it,” Sandler said. “You don’t notice it until it doesn’t work. It’s fundamental for protecting public health and safety. Not making investments now makes the investments more costly in the future.”

Dominic Fracassa is a San Francisco Chronicle staff writer. Email: dfracassa@sfchronicle.com Twitter: @dominicfracassa