Written by: Daniela Tapia Pitzzu

Illustrated by: Devon Hucek

Edited by: Sarah Bassiouni, Olivia Alge, Peijin Han, and Madeline Barron

During high school chemistry, my teacher gave the class a handout describing the perils of dihydrogen monoxide (DHMO). There were reports of DHMO causing suffocation, proving fatal if inhaled. This parody on water (which has the molecular name dihydrogen monoxide) was to advocate for science literacy. However, there was another buried message: even one of the most innocuous of chemicals can be dangerous if used improperly. 

Enter chloride. Not chlorine gas, not vinyl chloride, but sodium’s better half, the chloride in sodium chloride (table salt). 

In Michigan, the Department of Environment, Great Lakes, and Energy’s (EGLE) is starting to combat the increasing concentration of salt (salinization) in Michigan’s surface waters through its chloride water quality values. These aim to limit chloride discharge into Michigan’s surface waters which are important in preserving our freshwater ecosystems. It is important that we conserve the integrity of our freshwater systems, protect the flora and fauna that are too often victims of our carelessness and greed, and provide a clean and healthy water supply to everyone. 

Sources of Chloride

Chloride is ubiquitous. It’s in road salt applied to keep our roads safe in the winter, water softeners, processed foods, cleaning products, and with increasing frequency, in our surface and groundwater, both in Michigan and worldwide.

Of course, there are non-anthropogenic sources of chloride, including surface waters’ natural bedrock and atmospheric deposition. Nevertheless, chloride’s rampant use, especially with road salt, is driving concentrations to levels of concern in surface waters.

Harm to Aquatic Ecosystems

Excessive chloride concentrations in surface and groundwater pose immediate threats to aquatic ecosystems and by extension, our drinking water infrastructure. In aquatic ecosystems, the upward and downward movement of water, or vertical mixing, allows species to access nutrients. High conductivity, a consequence of increased chloride, inhibits this movement. Furthermore, some species are not equipped to handle increases in chloride and are outcompeted by invasive species or are pushed to extinction by a chloride-tolerant predator. Such impacts on the food web ultimately reduce biodiversity in these ecosystems. 

Threats to Public Health

It can be easy for some people to detach from problems they cause, as long as they are not affected individually. But, when it comes to chloride pollution, it does not work that way. The same water body affected by increased chloride from, for instance, road salts, could be your source of drinking water. A high concentration of chloride in water is associated with corrosivity and is indexed by the chloride-sulfate mass ratio The chloride-sulfate mass ratio (CSMR) is the concentration of chloride divided by the concentration of sulfate in the water stream. If the CSMR for a water stream is greater than 0.5, it can promote corrosion of lead pipes. According to the Environmental Protection Agency (EPA), concentrations greater than 0 mg/L of lead in water have adverse health consequences to human health and child cognitive development.  

Whether your water comes from a private well or a community supply, high chloride levels could release toxic metals into your drinking water; chloride concentrations are not monitored upon intake at water treatment facilities. Thus, the excess metal concentrations would only show up at a customer’s tap. Furthermore, while the EPA’s limit on chloride levels in the United States’ drinking water is enforced for taste, excess chloride in the human body may lead to hypertension, stroke, renal stones, and asthma. These look like the effects of a high sodium diet, but research has shown that sodium chloride, not just sodium is the culprit.

What Can You Do To Help?

Illustration by Devon Hucek

Reduce deicer use

In Ann Arbor, the Huron River Watershed Council (HWRC) provides a fountain of resources for how each one of us can reduce the salinization of our waterways.  These include suggestions for slippery driveways and sidewalks. Many of us use deicers or salt to keep our driveways and sidewalks safe. But what if we could use better products to keep our loved ones safe and protect our rivers from the threat of salinization? A video made by the Mississippi Watershed Management Organization details how to do just this. While I recommend watching the whole video, the key points are that if you must use a deicer salt after shoveling and sweeping your driveway/sidewalk:

  • Apply 4 lbs per 1,000 ft2
  • Use sand to avoid harming pets 
  • Only apply when it’s at least 0oF outside

Replace time-initiated regeneration water softeners

Another residential source of chloride is water softener regeneration. Water softeners run incoming water through a cation exchange resin containing sodium or potassium chloride. In the resin, cations contributing to hardness such as magnesium (Mg2+) and calcium (Ca2+) are exchanged for sodium (Na+) or potassium (K+). Eventually, the resin has no more sodium or potassium ions and needs to be washed to have its sodium/potassium ions replaced. This is known as “regeneration.” This salt solution is drained into the city sewer or septic system which eventually salinizes surface water or groundwater, respectively. 

The University of Minnesota Water Resources Center (WRC) has found that many old water softeners are time-initiated. This means that no matter how much water was softened, it will regenerate based on a set timer. If your residence or business depends on softening water, verify that the softener is not a time-initiated softener. If possible, replace with more efficient demand-initiated regeneration (DIR) softeners that regenerate depending on how much water is used. DIR softeners use 26-60% less salt than time-initiated regeneration softeners. In addition, they are water-saving and use 25-40% less water than time-initiated softeners. You can tell if your water softener is a DIR softener if there is a meter cable where the water flows from the softener and to indoor plumbing as shown below:

Photo courtesy of Tod Joseph

Spread the word and participate in citizen science

One thing anyone anywhere can do is spread the word (not the salt). I was introduced to this problem last year, as a graduate student! You can inform the newest generation, make it a family activity, or an outdoor activity for your classroom. The Izaak Walton League of America has launched a “Winter Salt Watch” kit to measure salt levels of streams and lakes near you. This is a citizen science approach where your results are uploaded to a shared database. 

All of Michigan’s inland freshwater surface waters drain to the Great Lakes. Thus, increasing chloride concentrations in inland lakes will cause salinization of the Great Lakes. Thirty million people, 10% of the United States’ population, and 30% of Canada’s population rely on the Great Lakes for their water supply. 


Desalinization is expensive. It is better to prevent salinization before it compromises the ecological health of the Great Lakes and the public health of those who rely on them for potable water. 

Let’s keep them unsalted and shark-free.

Daniela Tapia Pittzu is a graduate student in Environmental Engineering and Sustainable Systems at the University of Michigan. Her research and career interests lie in water quality and water pollution prevention. Prior to her life in Michigan, Daniela majored in Chemistry at the University of Nevada, Reno in her hometown and worked as a chemistry technician at Tesla’s Gigafactory in Sparks, Nevada. During her free time, she consumes books in fiction, social science, and science and technology, discovering new places in Ann Arbor, and playing with her fur ball Treme.

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