Ancient aqueducts famously feed water into Rome’s historic espresso bars. New York City’s tap water makes its pizza and bagels uniquely delicious — or so the story goes. And to some, San Francisco’s Hetch Hetchy water is sacred to making its sourdough bread, coffee and beer.

So with the city about to add groundwater to the pristine Hetch Hetchy mix, will these local specialties be forever tainted?

“It’s an honor and a privilege to do business and dwell in an area that has such great water,” said Nicholas Cho, co-owner of Wrecking Ball Coffee in San Francisco. “For the coffee people, or at least people really focused on quality, when the water changes, we know it. It’s a little bit like the weather for us.”

Cho is one of the food and drink industry folks who have been concerned about the San Francisco Public Utilities Commission plan to mix in a small percentage of groundwater, treated with chlorine for safety, to the existing water supply in 60 percent of the city next month. The initial change will be small and gradually increase over four years. While the pH level will stay the same, the added minerals will make the city’s typically soft water harder, which can affect flavor in coffee and beer, and texture in bread and bagels.

Before anyone panics, it’s important to know that the city’s water already isn’t as pure as a mountain stream. On average, 85 percent of our water comes from Hetch Hetchy and the surrounding lakes and reservoirs, which is soft due to the scrubbing it gets from flowing over Sierra granite; the other 15 percent comes from Bay Area reservoirs, which is harder. At the moment, the city isn’t even getting Hetch Hetchy water while repairs are being made on a mountain tunnel. Instead, all of it is coming from Bay Area reservoirs, said Jeff Gilman, hydrogeologist and groundwater project manager at the city PUC.

Mineral content and hardness is often measured as total dissolved solids in the water. San Francisco water is usually in the soft range of 45 to 50 TDS, and when all the groundwater is added, the range will increase to 70 to 120 TDS. (At the moment it’s at 120 or 125, Gilman says.)

In the coffee trade, higher TDS can change the flavor and can be hard, so to speak, on espresso machines and other equipment.

“We have always been aware of the effect water has on our coffee, and have done many tastings with different water over the years,” said Kyle Waters, lead equipment technician at Ritual Coffee Roasters, which has a cafe in the Haight-Ashbury, one of the neighborhoods that will get the new groundwater. “The TDS and hardness levels are something I’ll monitor closely as the program rolls out.”

For the true coffee water nerd — a term that surely applies to Christopher Hendon, an MIT chemist and co-author of the textbook “Water for Coffee” — it’s not just TDS, but specific mineral content that matters. The new water will have more calcium and magnesium, which can be beneficial, but also more bicarbonate, which can reduce acidity, a vital trait in coffee.

The San Francisco PUC said that normally, San Francisco’s water has 30 to 40 parts per million bicarbonate. With the groundwater fully added in, it will be 50 to 60 parts per million. A trained coffee taster can notice a difference when bicarbonate changes by only 5 parts per million, Hendon said.

“I would conclude that people might notice an appreciable difference in their coffee based on this data,” said Hendon. He joked, “It’s doomsday for San Francisco!”

Brewers aren’t feeling quite so apocalyptic.

“We seem to be spoiled with really nice brewing water,” said Kim Sturdavant, brewmaster of Social Kitchen & Brewery in the Sunset, who attended a meeting between brewers and the utility commission in December to learn about the water changes. “If a brewery isn’t using water filtration at the moment, now’s the time to think about getting it, to sort of buffer any variances that might be occurring.”

Depending on the style of beer, brewers often add minerals during beer making to balance the chemical composition or to mimic the beer’s traditional water source.

“It’s beneficial to have soft water for pilsner,” Sturdavant said. “Hard water works really well for hoppier beer.”

Hard water can be better for bakers, too — to a point. It can give dough structure, though too much can make it tough and limit fermentation. The new water’s composition keeps it in a good range for baking, although too many fluctuations can cause challenges, especially when you consider that bread is up to one-third water.

“When you’re a baker, you have so many kinds of forces in play, like humidity in the air and where you’re getting your flour from, since flour has seasonality as well,” said Amy Brown, who bakes several types of bread and bagels at Marla Bakery in the Richmond District, which will get the new groundwater. “It’s one more component that we’ll have to pay attention to.”

Hendon of MIT notes that several food-centric cities identify strongly with their water, especially when it’s soft, such as Melbourne, Australia, and Kyoto, Japan, as well as New York.

“San Francisco’s water is not particularly special,” Hendon said. “Everyone likes to think their water is special.”

Tara Duggan is a San Francisco Chronicle staff writer. Email: tduggan@sfchronicle.com Twitter: @taraduggan