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

An unseen person is holding some uncooked spaghetti pasta and dropping it into a pot of boiling water they have a salt shaker in their other hand.

Liudmila Chernetska/Getty

Key Takeaways

  • Adding salt to your pasta water is a common cooking practice that’s recommended in the instructions on many boxed noodles.
  • According to a new study, when chlorinated tap water is boiled with iodized salt and used to cook pasta, compounds are formed that could be harmful to consume. However, more studies are needed to find out if there are any actual health risks.
  • Choosing salt that isn't iodized, adding salt to your pasta after it is cooked instead of before it is boiled, or boiling your salted water without a lid may reduce the amount of these compounds that are formed during the pasta-cooking process.

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.

Why Is All This Stuff Added to My Water and Salt?

  • Iodine deficiency used to be a major public health problem in the United States, causing thyroid problems (goiters) in adults and impairing brain development in babies and kids. Adding a form of iodine (usually sodium iodide or potassium iodide) to table salt—something that most people had at home and regularly consumed—proved to be an effective way to increase the population’s iodine levels and prevent the health problems that deficiency had been causing.
  • Clean drinking water is another public health priority. That’s why chemicals like chlorine get added to a city’s water public water supply—it’s an effective way to make sure that the water that comes out of a home’s tap is safe to drink, cook with, and bathe in.

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.

How to Cook Safer Pasta

The researchers said these simple cooking tips can help reduce how much of those potentially toxic compounds end up on your pasta:

  • Take the lid off your pot when you’re boiling pasta
  • Strain the noodles from the water they’re cooked in
  • If you use iodized salt, add it after the pasta is cooked
  • If you want to salt your pasta water for cooking use iodine-free salt like kosher and Himalayan

“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.

What This Means For You

If you are concerned about the compounds that are formed when pasta is cooked, avoiding adding salt to your boiling water, cooking pasta without a lid, or opting for an iodine-free salt can allow you to enjoy pasta with fewer of these compounds.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Croce L, Chiovato L, Tonacchera M, et al. Iodine status and supplementation in pregnancy: an overview of the evidence provided by meta-analyses. Rev Endocr Metab Disord. 2023;24(2):241-250. doi:10.1007/s11154-022-09760-7

  3. National Cancer Institute Division of Cancer Epidemiology and Genetics. Drinking water contaminants.

  4. Li XF, Mitch WA. Drinking water disinfection byproducts (DBPs) and human health effects: multidisciplinary challenges and opportunitiesEnviron Sci Technol. 2018;52(4):1681-1689. doi:10.1021/acs.est.7b05440

  5. American Chemical Society. Four ways to reduce unwanted iodized table salt reactions when boiling pasta.