With more than 30 years’ experience in the residential and commercial water treatment space, Mark Nelson is a Class 1 Drinking-Water Operator and a CBWA (Canadian Bottled Water Association) Certified Plant Operator. As founder and president of Nelson Water in Ottawa, Mark focuses on dealing with challenging water treatment system designs for problem water. He also heads the largest water bottling plant in the city of Ottawa with a delivery network throughout the Valley.

Let’s face it, a car represents a significant investment, and the condition of the paint protects the car from corrosion. So, it makes great sense to keep your car free from abrasive dirt, bird droppings, and sticky leaf sap that can damage your paint, But, when it comes to washing your car, is it a better idea to use soft water?

Water Hardness and Car Washing

It is perfectly possible to wash your car with any clean source of water. Generally speaking, people tend to use one of three different types of water to wash their car, they are: soft water, hard water, and reverse osmosis (RO) water. If you have hard water in your home, you may already have noticed the water spots on the surface of your plumbing fixtures and shower stall. These are caused by the mineral content left behind from hard water when the water has evaporated away.

Hard water has an elevated concentration of minerals, including calcium, magnesium, and to a lesser extent, iron. But, these are only part of the problem; the total mineral content or “Total Dissolved Solids” as it is referred to in the water treatment industry, can be a real indicator of a water source’s potential to create water spots. As a rule, the higher the TDS, the more water spots you will find after cleaning.

When it comes to your plumbing fixtures and fittings, it is possible to get rid of the chalky white mineral deposits. Simply spray the area with white vinegar, leave it for a while and apply plenty of elbow grease. The water spots will return eventually because the underlying water hardness issue has not been addressed. But, the area will be clean for a while, and then you will have to repeat the process. Obviously, this type of cleaning regimen will only damage the car paint. So, what happens when you clean a car with hard water?

Washing Your Car with Hard Water

As we’ve seen, using hard water in your home can cause a number of cleaning and rinsing problems. It is also true that the elevated mineral content does inhibit the formation of soap suds in detergents. Some people attempt to mitigate this by simply adding more detergent to the water, but this is ineffective. If you attempt to use more soap or detergent to wash with hard water, you are simply throwing money down the drain.

These issues are equally applicable when it comes to washing your car with hard water. Some people try to use a pre-soak or add more car washing detergent to get their car clean and free from water spots. But, aside from the problems we have already discussed, there are some strange quirks when it comes to car washing with hard water. Although you can wash your car in hard water, the mineral content will cause other issues, most notably spotting. But, when it comes to using drying agents or a good quality car wax, these products actually work better after a hard water wash.

The chemical composition of car wax and a drying agent will not react with hard water components. Out of the three types of water used for car washing, hard water has the highest surface tension because of the elevated mineral content. This makes the water easier to remove when it comes to drying and waxing later. Because hard water has very little contact or adhesion to the surface of the paint, the drops of water are easy to blow away when drying.

Soft Water Car Washing

Many car owners notice the water spots after a car wash and wax, and they often blame hard water for the problem. This and other hard water problems in the home then prompt them to seek out a solution. The best way to deal with a hard water problem in your home is to install a water softener. But, if you make the switch to car washing with soft water, will this produce better results?

The short answer is probably because a water softener may not be able to remove the mineral content that is causing the formation of water spots. Most modern and effective water softeners use an ion exchange system. This works by taking the ions of hard water minerals such as calcium and exchanging them for benign sodium (salt) ions. But, the mineral content is only part of the problem; the Total Dissolved Solids (TDS) of soft water is pretty much the same as hard water.

Essentially, softer water has less calcium, magnesium, and iron and higher salt content. So, washing your car with softened water will remove scaling in your home, but if you have a high TDS level, you may still get water spots on your car after washing. But, it will be easier to remove those water spots later because they are softer, and they are easy to wipe off the surface.

Although there are more sodium ions present in softened water and it is technically saltier, the quantities added are negligible. Remember that we’re talking about an ion exchange process, which is minuscule amounts of salt. Softer water works better with presoaks and detergents, and you don’t need to use as much. Many users are surprised at the difference after they make the switch and rinse their car for the first time. As we discussed earlier, waxes do perform better with hard water, but a little extra elbow grease will go a long way to fixing this problem.

What About Reverse Osmosis Water?

Many people have a water softener to exchange the mineral ions for sodium and an RO system that then removes any added salt. This really is the best of both worlds because you have water that is pure and easier to work with. The water is forced through a semi-permeable membrane to remove any contaminants. No chemicals are used during this process, and RO water ideal for car washing and rinsing because this process lowers the TDS too. There is no need to rinse away any water spots when RO water has been used because nothing is left behind when the water evaporates.

Contact a local water treatment specialist for expert advice.