Addressing hard questions about Thornton’s water

 In Water Hardness, Water Quality, Water Treatment

Learning more about Thornton’s water quality, treatment and technology

What is water hardness?

Water hardness is a measure of the amount of dissolved minerals, largely calcium and magnesium, which naturally occur in water. Hard water does not mean “bad” water. Perrier sparkling water is harder than Thornton’s water!

Is Thornton’s water hard?

Generally speaking, Thornton’s water is in the mid-to-high range of water hardness. Thornton’s water hardness can vary greatly during the year. In 2020 for example, hardness varied between 104 and 330 milligrams per liter. These values are typical of water systems in the western United States, but slightly higher than in 2019 due to drought conditions.

What are some effects of hard water?

When hard water is heated, solid deposits of calcium carbonate can form. It can cause mineral buildup in faucets, showerheads and plumbing. It can create spotting on glassware and can increase the need to clean filters more often in appliances such as dishwashers and clothes washers. Soap reacts with the calcium in water and can form “soap scum”. More scrubbing of fixtures, hands, dishes or laundry may be necessary to keep things buildup-free.

Is the hardness of our water safe to drink?

Thornton’s water is safe to drink. People need minerals to stay healthy. The World Health Organization (WHO) states that drinking water may be an important contributor of calcium and magnesium to your diet. Minerals and nutrients are measured as Total Dissolved Solids (TDS) in parts per million (ppm). While TDS in water do not create a health risk, the Environmental Protection Agency (EPA) suggests a maximum of 500 ppm. The TDS in Thornton’s water averages 300 ppm, well within state and federal safety standards.

Why doesn’t the city soften our water?

The largest use of Thornton’s water is outdoor irrigation so the extreme cost of softening water before it leaves the treatment plant is not an efficient use of our customers’ investment. “Point of use” is the most cost-effective approach. This is similar to why Thornton does not provide hot water to the entire city as homes have individual water heaters. Another consideration is that soft water can be very corrosive to metal pipes and appliances, putting drinking water at higher risk of containing copper over time.

How does the city address the hardness of our water?

To help counter the higher mineral concentrations, water treatment staff use a blending technique that combines water sources with less mineral content such as Upper Clear Creek, via Standley Lake storage, with higher mineral content sources such as Lower Clear Creek and South Platte. In the future, blending water from the Cache la Poudre is also expected to improve water hardness.

How does the hardness of Thornton’s water compare to other cities?

It is estimated that 85% of the U.S. has hard water with a high concentration in the central and mid-west regions.

Water Hardness Map
This map illustrates the concentration of calcium in water sources by state. Because of Colorado’s semi-arid climate, our Front Range has harder water relative to the coastal regions. Source: U.S. Geological Survey

What can I do?

There are ways to outsmart hard water. Create your own cleaner by mixing 50/50 distilled water and white vinegar or vinegar with baking soda. Use it to clean faucets, showerheads, bathtubs, sinks and more. You can also run diluted vinegar through your coffee maker to prevent buildup. Lemon juice can also cut through mineral deposits on water fixtures because of its acidity. For your dishwasher, try adding a splash of white vinegar in the bottom before you run a load. Cleaning the dishwasher’s filter regularly helps reduce spotting. Chemical cleaners can also help eliminate scale buildup and rust stains.

For a more permanent solution, there are a variety of residential water softeners that can be installed to prevent some of the challenges hard water presents. Just remember to maintain softener systems regularly to ensure they are working properly.

Where can I learn more?

Our 2021 Water Quality Report provides water customers with details about Thornton’s most recent water quality data. Visit to learn more or track the City of Thornton’s water efficiency and water quality programs at

Without Water Life Would Be Pretty Dry graphic
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