Is Soft Water Good for Washing Cars?

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Wondering whether hard water or softened water is best for getting your car properly clean and spot-free during a wash?

In this guide, we’ve answered the common question: “Is soft water good for washing cars?”

πŸ“Œ Key Takeaways:

  • Soft water is better than hard water for car washing because it doesn’t form mineral deposits on surfaces.
  • However, softened water may still leave spots caused by TDS.
  • The best type of water to use for washing a car is reverse osmosis water, which contains no calcium and magnesium ions and no TDS.

πŸ€” Is Soft Water Better For Washing Cars? Overview

Soft water can be better for washing cars, but it won’t necessarily give you the cleanest end result. While soft water doesn’t contain scale-causing minerals, it’ll likely still contain total dissolved solids (TDS), which means you won’t achieve a spot-free rinse even if your water is softened.

❔ What Is Soft Water?

Soft water is water with low water hardness.

Water hardness is a measure of water’s calcium and magnesium content. The more calcium and magnesium minerals water contains, the harder it is.

Sometimes, water may be naturally soft, meaning that it’s naturally low in hardness minerals. Other times, water may be softened by a water softener, meaning that its calcium and magnesium minerals have been removed and exchanged with sodium.

Water hardness matters for washing cars because water’s mineral content affects your end results. The harder your water, the more spots and mineral deposits will linger on your car’s surface after washing.

Using water while regeneration takes place

πŸ†š Washing Your Car With Hard Vs Soft Water

Let’s take a look at the differences between washing your car with hard water and washing your car with soft water.

Car Wash With Hard Water

When you wash a car with hard water, you’ll notice spotting and mineral deposits on your car’s surface after rinsing, which are caused by the hard water mineral ions (magnesium and calcium).

You will also need to use more soap to achieve the same clean result when washing your car with hard water because the hardness minerals reduce water’s ability to lather with soap, reducing soap suds formation.

However, it’s not all bad. Certain products, including car wax and drying agents, actually work better when they’re used alongside hard water. The chemical compositions of these products don’t react with hardness minerals, and because of hard water’s high surface tension, it’s easy to remove the water when drying and waxing the car at the end of the wash.

Car Wash With Soft Water

When you wash your car with soft water, you should get a slightly better end result because soft water has a low hardness mineral content. That means you’ve removed the components of your water that lead to scale formation.

Soft water also works better with detergents and soaps, and you can achieve the same end result by using less soap. As we mentioned above, using waxes is easier with hard water, but you can still use wax with soft water as long as you put in a bit of extra effort.

However, a car wash with softened water won’t lead to a completely spot-free rinse because soft water still contains total dissolved solids (TDS), which are also responsible for spotting on surfaces.

Plus, salt-softened water contains sodium salts, which may have their own effects on the quality of the final rinse. While water softened by ion exchange only contains very low salt levels, salt is a corrosive contaminant and there’s always a chance that it could cause certain areas of your car to rust.

So, softened, high-TDS water isn’t quite the solution for washing your car, but it certainly produces a better outcome than using untreated water hardness minerals in your washing formula.

Washing car with soft water

πŸ‘ Benefits Of Using Soft Water For Car Wash

Now we know the differences between using hard and softened water when washing your car, let’s take a look at some of the benefits of using softened water for a car wash.

Reduced Mineral Buildup

The biggest benefit of using softened water for car washing is that you should notice a reduced mineral buildup on your car’s surface.

Water treated by a water softener no longer contains calcium and magnesium hardness ions, so it won’t leave mineral deposits when the water evaporates.

Better Cleaning Performance

Softened water lathers better with soaps than hard water, so you should get better cleaning from your car washing products than you would normally.

You can also use less soap than usual to achieve the same results, so you can save money by reducing your soap consumption.

Less Water Spotting

Unlike hardness ions, sodium salts don’t leave limescale deposits on surfaces. So, using softened water for car washing should reduce the overall spotting on the surface of your car after a wash.

However, softened water doesn’t guarantee a spot-free wash, as we’ve discussed in more detail later.

Before and after washing with soft water

Longer Lifespan Of Car Paint

Softened water can also extend the lifespan of the paint on your car.

Hard water droplets eventually dry and leave mineral deposits on your car that can affect the paintwork and reduce its lifespan.

Using softened water, on the other hand, doesn’t leave deposits when the water evaporates, so you can retain the color and quality of your car paint for longer.

πŸ‘Ž Drawbacks of using soft water for washing cars

There are a few setbacks of using soft car wash water that you should also know about:

Doesn’t Guarantee A Spot-Free Finish

Car washing spots occur as a result of all manner of total dissolved solids (TDS) in water, so even if you reduce your water hardness mineral content, other dissolved solids in your water could still form spots on your vehicle’s finish.

The only way to avoid this is to install an RO system or buy bottled reverse osmosis water.

Softening Water Can Be Expensive

Installing a water softener can help you save money on soaps and improved appliance efficiency in the long run, but the upfront cost of this water treatment system can be quite high.

You’ll need to save around $800-$1,200 for a water softener, excluding the cost of installation.

🚘 How To Maximize The Benefits Of Soft Water Car Washing: Use RO Water

So, soft water is the better alternative to hard water for washing your car, but it still won’t give you a completely soft-free rinse.

The best way to get the best quality wash is to use soft, TDS-free water (essentially pure water).

You can use a reverse osmosis water system to treat your home’s softened tap water, or purchase reverse osmosis water in bottles to wash your car.

RO water doesn’t have a high hardness or TDS level. It doesn’t contain any minerals or salts that could leave deposits on your car or react with any of the soaps and detergents used to wash your car.

Plus, RO water displaces wax droplets, leaving no wax behind, and there should be no spots formed by any of the unrinsed droplets.

Usws defender whole house ro system after installation

πŸ“‘ Final Word

So, softer water does yield better results, but remember that hardness deposits are only a part of the problem if you’re noticing spotting at the end of the carwash process.

If you don’t currently know what your water contains, start there. Buy a hard water test kit and a TDS meter to find out the likely causes of the water spots on your car after washing.

  • Laura Shallcross
    Senior Editor

    Laura is a passionate residential water treatment journalist who holds an undergraduate degree in Print Journalism and a master’s degree in Creative Writing. Over a span of 5 years she's written on a range of topics including water softening, well water treatment, and purification processes.

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