Does CLR Remove Hard Water Stains? Our Investigation

In this article, we investigate how well CLR (Calcium, Lime, Rust) works on tough hard water stains such as those caused by calcium, lime, and iron oxide, its composition, and uses. An understanding of hard water is important when trying to find a product that will be effective where most other soaps and detergents fall short.

Several products on the market do the job of removing mineral deposits (limescale) and soap scum that have varying degrees of success. We discuss the pros and cons of CLR Some precautions and safety tips are given for when using CLR and other chemical cleaners.

Most importantly, this article will explore the pros and cons of this product and how effective CLR is as a remover of hard water stains.

Hard Water

Water is considered hard if it has a high mineral content when water filters through gypsum, chalk, and limestone made up of mostly calcium or magnesium ions. These minerals dissolve and flow out with the water. In your home, you can tell water is hard when soap does not form foam when agitated in water.

Permanently Hard Water can be determined when the concentration of cations has charges greater or equal to 2+. e.g., Ca2+ and Mg2+. This water is filtered through rock such as limestone, igneous, or dolomite. Groundwater is more typically hard, having percolated through mineral-rich rock, whereas rainwater is softer, containing less mineral content. Needless to say, if you have borehole water, it will likely be hard. Permanent hardness can unfortunately not be removed by boiling as calcium and/or magnesium ions do not filter out with heat.

Temporary hard water contains dissolved bicarbonate minerals. Unlike permanently hard water, temporary hard water can be softened by boiling or adding lime. Boiling precipitates calcium or magnesium carbonate out of the water, leaving it softer once it has cooled.

Hard Water Stains

Hard water stains are caused by precipitated minerals that build up over time and may clog up plumbing and cause unsightly stains. This precipitate is named calcium stearate, which is a calcium salt compound mixed with solid organic acids. It is a very stable compound even under high temperatures, and sometimes even used as a food additive E470. It has water-repellent properties and is therefore resistant to water. It is used in various processes as a thickener, stabilizer, or lubricant.

Hard water stains, also known as hard water deposits, mineral buildup deposits, or limescale, appear as a whitish, chalky type of residue wherever hard water is used. There are two types of hard water stains, limescale and soap scum.


Limescale is pervasive where hard water and heat are found, such as in bathrooms and kitchens, heaters, and other areas of high humidity. This menace builds up and can clog up pipes. Taps (faucets) can become encrusted quite quickly with this white powdery residue. Although limescale is not harmful to humans, and, in some cases beneficial, it can cause water spots and stains and can damage appliances such as coffee percolators and kettles.

Soap Scum

Hard water tends to produce a white precipitate (soap scum) rather than a lather when mixed with a soapy product (soaps and detergents) that contains sodium stearate as its main component. The precipitate and soap do not mix well due to the interaction between the fatty acids in the soap and the minerals in the water. This soap scum is an ideal environment for the growth of mold and mildew. Apart from looking unpleasant, mold spores are one of the main problems for people who suffer from allergies.

What is CLR?

Enter CLR. A product that efficiently removes deposits and stains from hard water and soap scum. CLR stands for Calcium, Lime, and Rust. It is a household cleaning product made from water, lactic acid, citric acid, gluconic acid, surfactants, and sulfamic acid. This formula is versatile, removing various difficult stains, is environmentally friendly and antibacterial, and comes in industrial strength and for household use.

What is CLR Used For?

CLR tackles those stubborn stains on your bathroom tiles, shower walls, and showerheads, bathtubs, and toilets. It can also be used on surfaces such as porcelain, stainless steel, chrome, glass, cement, ceramic, fiberglass, brick, and plastic. Use it to clean appliance exteriors like your washing machine, dishwasher, humidifier, toaster, and kettle. CLR can also be used to clean off grease oil residue and water spots.

How Does CLR Work?

The different kinds of acids in CLR contain certain compounds and aspects and are used for specific purposes. Water prevents the solution from being too toxic, by diluting the acids. Gluconic acid dissolves mineral deposits and lifts and removes stains. Sulfamic acid cleans metal and removes rust. Lactic acid prevents the solution from dissolving too quickly and citric acid softens water and gives it a pleasant odor.

So, Does CLR Really Work?

CLR has been reviewed by several people and has been rated 4 or 5 stars on Amazon. Customer reviews are a good way of discovering other people’s opinions on a product. One consumer said that CLR is more powerful than most de-scalers and may not leave as much discoloration. Depending on your particular usage, you should consider whether CLR is a good fit. Other reviews say it is a good product that is effective and requires little scrubbing to remove scale and stains.

If you don’t trust these reviews ask around from people you know. Ultimately the best way to ensure the product is useful to you is to buy some and use it yourself. Be aware of the safety precautions recommended on the container and in articles and reviews on the product.

Here is a summary of the pros and cons of CLR


  • Very effective
  • More environmentally friendly than some products on the market
  • Non-toxic in recommended dosage
  • Can and should be diluted.
  • Optimum performance in 2 minutes
  • Can be used on several surfaces such as metal, plastic, tile, and ceramic.


  • Contains acids, so can be dangerous if consumed.
  • Releases fumes
  • Cannot be used in a spray bottle.
  • Not suitable for surfaces such as wood, clothing, carpets, or natural stone


Even though CLR is considered safe to use, consider these precautions:

  • Do not mix CLR or use it with any other products especially if they contain ammonia or bleach.
  • Although it is non-toxic, always wear gloves when handling all cleaners.
  • Keep away from pets and children.
  • This product may be diluted and therefore be left on surfaces for a short while longer. The recommended dilution is one part CLR to one part water.
  • Always use in a ventilated area.
  • Do not breathe in fumes for long periods.
  • Do not use it in a spray bottle as this can cause additional fumes. Place cleaner in a bowl and apply with a sponge or scrubbing brush.
  • Spot test on surfaces first before cleaning.
  • Clean spills immediately on surfaces that are not suitable for this product.
  • Do not leave on surfaces for longer than a couple of minutes.
  • Rinse surfaces with water after cleaning.

Do Not Use CLR on these surfaces

Because CLR is acidic, it can cause damage to certain surfaces. It should not be used on:

  • Wood
  • Clothing
  • Wallpaper
  • Carpets, rugs and mats
  • Natural stone e.g. granite and marble
  • Brass
  • Copper
  • Aluminum
  • Galvanizing
  • Painted, coated, or sealed surfaces.


In areas of the world where there is scarce or very variable rainfall, many people rely on groundwater for their survival. This can be a blessing and a curse. Groundwater is full of minerals such as calcium and magnesium, which we need to remain healthy. On the other hand, mineral deposits can build up on pipes, bathroom and kitchen tiles, inside appliances, and in other areas of moisture and heat.

This mineral-rich water known as hard water, can cause stains. De-scaler products are the only effective way of removing this residue and discoloration. Various lime-rich products do the job of cleaning these stains, but CLR has good reviews for its potency. Being non-toxic, it is the go-to product for those who wish to use something environmentally friendly but stronger than other natural acids like vinegar.

When handling all cleaning products, even the safe ones, it is important to wear protective gloves and prevent yourself from breathing in fumes. Follow the instructions on the container carefully to avoid any accidents or using the product on surfaces that are unsuitable for CLR or other chemicals.