Differences Between Calcium and Lime Deposits in Toilets

Differences Between Calcium and Lime Deposits in Toilets. Cleaning toilets is an essential part of keeping your home safe and sanitary, but it is a task made more difficult by the mineral deposits that can sometimes collect on and inside toilets. Calcium and lime deposits are among the most common minerals encountered by homeowners cleaning bathrooms, and understanding how they make their way into your toilet and how they differ from one another can greatly assist in effectively removing them.

Water Hardness

Household water is called hard when it has high levels of calcium and magnesium. The presence of these minerals in their +2 cation form makes many household tasks involving water more difficult. Soap does not lather as well in hard water showers, for example. A specific chemical reaction that takes place when mineral deposits react with hot water creates a material called scale, a hard, difficult-to-remove mineral deposit on the surface of the vessel that came into contact with the mineral and water.

Calcium Deposits

More specifically, the hard deposits you see on your toilet and dishes are known as precipitates, results of an ionic chemical reaction that produces insoluble precipitates. The calcium carbonate precipitate (calcium deposit) is formed when hard water is heated and calcium ions react with bicarbonate ions to form insoluble calcium carbonate.

Lime Scale

When the same aforementioned chemical reaction involves both calcium and magnesium, it can produce lime scale deposits. Just like calcium scale, lime scale makes cleaning toilets more difficult because lime scale clings tightly to surfaces and cannot be removed with a typical scrubber or sponge. To effectively clean lime scale or calcium carbonate scale requires a class of cleaning chemicals known as sequestrants. Those sequestrants such as Calgon deactivate minerals so that they do not cling to surfaces so tightly and can be more easily cleaned.

Softening Water

Using sequestrants to clean mineral deposits is more of a temporary solution since deposits will continue to collect on the toilet as long as hard water is running through the toilet's plumbing. Many different techniques can be used for softening water, ranging from simple chemical additives to large-scale water softeners that integrate with a home's plumbing to remove magnesium and calcium deposits from the entire home's water supply.


  • North Carolina State University Extension; Removing Mineral Deposits From Household Surfaces; Sandra A. Zaslow
  • Washington University in St. Louis; Water HardnessRachel Casiday & Regina Frey