You May Want to Rethink Salting Your Pasta Water If You Use Tap Water

If you’re craving pasta for dinner, the sequence of grabbing a pot, filling it with tap water, and adding salt is probably something you can do on autopilot. Salting pasta water is a tried-and-true way to improve the flavor of each noodle.

When you pour the noodles into the boiling water, you’re probably not thinking about all the chemical reactions that are about to take place to turn those strands into a tasty meal—but according to a new study, maybe you should.

Researchers from the University of South Carolina found that the process that many of us have always used to cook pasta can create some chemical reactions that could be concerning.

Here’s what you should know about the science behind iodized salt and tap water, and what it means for cooking up your favorite noodles.

What Happens When You Boil Tap Water With Iodized Salt?

The two key pieces of the pasta-cooking conundrum presented in the new study are iodized table salt and chlorinated tap water.

When you’re boiling water for pasta, you’re probably just using regular tap water. If you’re hooked up to your city’s public water supply, chances are your tap water is chlorinated to help keep it safe.

Adding salt to pasta water gives each noodle a chance to absorb some of the salty taste as it cooks, which enhances the flavor of the final dish. The salt in your salt shaker is probably iodized, which means it’s had a key nutrient called iodine (in the form of iodide) added to it to help prevent iodine deficiency.

Cooking pasta in boiling chlorinated tap water with added iodized salt may lead to the formation of compounds called iodinated disinfection byproducts (iodo-DBPs).

Previous studies have suggested that long-term exposure to drinking water with high amounts of these byproducts might be linked to rectal and bladder cancers.

Testing 'Real-World' Pasta Cooking Conditions

Previous research did not look at “real-world” cooking conditions—that is, what people are doing in their home kitchens as opposed to what researchers do in a controlled lab.

That’s what the researchers who did the latest study set out to test.

In the first experiment, the researchers boiled the pasta according to the directions on the package and used table salt with added iodine. In the other tests, they changed the cooking conditions and used different kinds of salt (e.g., kosher, Himalayan) that did not have added iodine.

For each cooking method, the team measured the amounts of six “potentially toxic compounds” called iodinated trihalomethanes in the cooked pasta as well as the water.

While the researchers did find all six of the compounds in the cooked noodles and the pasta water, they also noted that the way the pasta was cooked had a clear effect on how much of those compounds were in the final product. 

Susan Richardson, PhD, a professor of chemistry at the University of South Carolina and one of the study's authors, told Verywell that a surprising finding from the experiments was how few of the iodo-DBPs sorbed or “stuck” to the pasta compared to how much was drained out in the water.

“I was surprised that 70% of the iodo-DBPs were ‘washed away’ in the strained water,” she said. She expected the pasta would soak up almost 100% of the compounds.

Can You Cook Pasta In Salted Water or Not?

Richardson said that pasta lovers do not need to panic over the study’s results.

“The levels [of the compounds found on the tested pasta] are lower compared to some drinking waters that are impacted by iodide,” she said.”

While more research is needed, Richardson thinks that iodo-DBPs “are of concern.” Personally, Richard said she is likely going to start using iodide-free salt to cook pasta from now on.

“While this paper is interesting, it doesn’t demonstrate any kind of human interaction or harm,” Idrees Mughal, MBBS, a Britain-based physician with a master’s in nutritional research, told Verywell.

Richardson confirmed that we don’t know the potential health effects of these compounds yet, “since the in vivo toxicology studies are not done yet.” While bladder cancer could be a risk of long-term exposure, research is needed to understand the risk.

Mughal said that if people are truly concerned, keeping the lid off of the pot while their pasta is cooking or using the other tricks the authors suggested will probably help.

Bottom line? Until researchers look at the effects of ingesting these compounds in the amounts found in a typical pot of noodles, you do not need to stop eating pasta or change how you cook it.

You also do not need to swap iodized salt for iodine-free salt for everything—you just may not want to use it for cooking pasta.

While it could contribute to a chemical reaction when it is used to cook up noodles, iodized salt is still a key source of the nutrient in our diets and helps prevent deficiency—a health consequence that is well-known and backed up by research.