How to Soften Hard Water to Wash Car? – 3 Methods

Written by

Bruce Sonnier


Marcus Dutton

how to soften hard water to wash car

If you’ve been washing your own car and have had issues with car soap that doesn’t lather well or water spots forming no matter the materials or brands you’ve used, that means you must’ve been washing car with hard water.

Don’t worry! Reducing the hardness of water and using soft water for washing cars is easy.

This article will guide you on how to soften hard water to wash car so you can efficiently give your car that spotless look.


Methods to Soften Hard Water to Wash Car

Option 1: Boil the water beforehand


What to prepare:

  • Pot of water

Hard water contains minerals that cause water spots and the lessened efficacy of soap. Boiling hard water will break down and precipitate the minerals that are in it leaving the water softer.

Make sure to wait for the water to become room temperature before you use it. Then proceed to wash your car as usual.

Option 2: Use white vinegar or lemon juice


What to prepare:

  • 1 cup of vinegar or a few tablespoons of lemon juice
  • Bucket of water

Vinegar and lemon juice are both acidic, while mineral deposits in hard water are alkaline. Mixing the two together will neutralize the water and lessen its hardness.

Simply mix the vinegar or lemon juice with water, then use this solution to wash your car as you normally would.

Option 3: Use a hard water filter


There are a lot of hard water filters available in the market. Below are two options to choose from.

1. Use a cheap in line water filter

Investing in a water softener for washing cars does not have to be expensive. You could buy a cheap in line water softener or filter for your car for less than $20.

What to prepare:

  • In-line water filter
  • Water hose (optional)
  • Empty buckets

To install this type of in-line water filter, screw the filter directly onto the water spigot or faucet by twisting. Make sure that the filter is hanging tightly to ensure no leaks.

You can connect the end of the filter to a water hose or let the water go straight to a bucket. Turn on the water and let it run for 5 to 10 minutes to start filtering all the hard minerals.

Once you’re done installing this type of water filter, you can begin to use it to wash your car.

2. Use a hard water filter for pressure washer

Before you buy a pressure washer, or if you already have one, you should also consider investing in a car wash hard water filter to use alongside it.

This type of water filter is also an in-line water filter, but they are more expensive than the one above. Below are some things to consider when choosing the right filter for you:

  • Size

You should consider how hard the water is in your area. Also, consider how many cars you’ll wash and how often you’ll do it.

Do note that the filter material inside the filtration system can be replaced. You don’t have to buy a new machine every time you go through hundreds of gallons of water.

  • Compatibility

Make sure that your pressure washer and water filter are compatible. The pressure washer should be the most gallons per minute of water output that the hard water filter can process.

If you still need clarification as to which filter to choose, you can browse through car-related subs on Reddit like r/AutoDetailing, to see honest feedback from car enthusiasts.

  • Ease of replacement of inside filter

Some have filter material that comes prepared inside canisters only. Still, if you want to save money, you can buy the filter material in bulk and put it inside the canisters yourself. Not all filters have this option.

To know when you have to change the inside filter material, some water filters come with built-in Total Dissolved Solids (TDS) monitors. The number on the monitor should generally be below 10.

Once it goes higher and reaches the hundreds, it means it’s time to replace the inside filter. Not all water filters come with a built-in TDS monitor.

Although there are different brands of filters, they have the same basic setup. To use this type of hard water filter:

  • Attach the water inlet hose of the water filter to the water spigot or faucet
  • Use the water hose to connect to the pressure washer on the outlet side. If you don’t have a pressure washer, you can use the hose nozzle directly.
  • Once you’re done installing, you have to turn on the water and you can immediately wash your car.

What Happens to Use Hard Water to Wash the Car?


  • Car soap or shampoo doesn’t lather easily

When you use hard water on car instead of soft water, it lessens the efficiency of car soap or shampoo.

Water is considered hard water when it reaches a certain amount of minerals per liter, mainly calcium and magnesium ions. How hard water is will differ per area and even per season.

When used with soap, the minerals in the water react by creating film-like soap scum (also called lime soap) instead of just soap foam. The harder the water, the less soap will lather.

Using hard water during a car wash means using more soap to make it foam.

  • Hard water leaves water marks on cars

Hard water has many mineral deposits that leave traces on the car once the water evaporates. These are what create the very unsightly watermarks.

If you use hard water, it also means having to use more water to continually mist the car and avoid the formation of water spots while cleaning. There’s also a chance of doing a complete rewash if the hard water dries up quickly when washing under the sun.

How Can Water Softening Benefit Car Wash?


  • No water spots on cars

Water softening is great for car washing as soft water helps avoid water spots when washing car.

Water softener filters exchange the calcium and magnesium ions in hard water with sodium ions, creating soft deionized (DI) water. The absence of these minerals means that once the water evaporates, there will be no mineral traces left to leave marks on your car.

  • Less car soap or shampoo is needed for a wash

Soap scum will not form as an unwanted chemical reaction if there is an absence of hard minerals in the water. Car soap or shampoo can do its job more efficiently and lather easily.

Since foam forms easily, less car soap or shampoo is needed, and rinsing off the foam will be easier as no extra minerals need to be washed off.


Now that you know how to soften hard water to wash car and its benefits, your car washing experience can now be much more efficient.

Spending money on a hard water filter for washing cars might be an extra investment, but it sure is a good one. In the long run, it will save you time, energy, and money as now you’ll spend less soap, water, and effort when you wash your car.

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