Water Spots and Streaks on Cars and Windows?

Water Spots and Streaks on Cars and Windows?


I have spots or streaks on my car/windows. How can I remove them?

To provide a very short summary; there are many different minerals in your water supply that cause these spots and streaks, which leave residue behind when they dry.  Here at PumpExpress, we offer a water filter that will remove the mineral content from the water leaving you with an immaculate finish every time as well as saving you money on expensive wax and polish. Below is our range of crystal water filters, these are specifically designed to be a plug-and-play.

A photo of a blue car wash filter tank at 8l capacity.

Crystal Water Filter – For Cars and Windows – 6L

A photo of a blue car wash filter tank at 8l capacity.

Crystal Water Filter – For Cars and Windows – 12.5L

A photo of a blue car wash filter tank at 8l capacity.

Crystal Water Filter – For Cars and Windows – 25L

A deeper look into why this occurs.

If you have ever washed your cars or windows, you are all too accustomed to the odd water spot or streak across your otherwise immaculate finish. This may leave you wondering: what causes these marks on your car and glass windows, and can you do anything about it? When water droplets dry on your car or windows they leave a residue behind, mostly containing a wide assortment of minerals.  

The density of these minerals roughly determines how hard or soft the water is.

Rainwater is typically considered soft water due to its low concentration of minerals and high concentration of salts and gases from the atmosphere. This salt content often causes water streaks and spots when it dries on your windows or car surfaces. 

Hard and Soft Water: 

Hard water contains large amounts of calcium, magnesium, iron, and other minerals; higher densities change the water’s PH, making it harder. Many people use water softener systems in their homes and businesses to reduce hard water and make it softer. Soft water typically contains more sodium content and is preferred for people who wish to protect white goods or have skin conditions that require it.

How can I tell if I have soft or hard water? 

Hard water will often result in a film on your hands after washing them due to the soap reacting with calcium to form soap scum. The additional minerals form water spots on glasses and silverware after washing them or finding mineral stains on clothes. Soft water has more benefits, such as soap that is easier to lather when washing clothes, dishes, and even hands or bodies, with less soap overall being needed. However, the easiest way to tell is to simply do a hard water test, which is readily available to buy.


The effect of UV on dried residue:

As water droplets dry on a car or glass surface, UV rays from the incoming sunlight react with the minerals, causing a chemical reaction that results in them becoming bonded to the surface. The type of chemical bond and how hard it is to remove depends on the minerals in the droplet.

How can I sort this problem then?

The simplest way is to get a water softener or filter that removes all of the minerals from the water. If you have a car you want to keep streak-free, we would recommend keeping it in a garage or overhead shelter to protect it from rain, wind, and dust storms. Alternatively, after drying the car, you could also use a soft fabric car cover along with wax or ceramic polish for further protection.


At PumpExpress, we provide a range of crystal water filters for cars and windows. Our water filter capacities range from six liters up to twenty-five liters. The filter provides ultra-pure water for the washing of cars and windows, leaving no spots or streaks behind for a perfect finish.

If you have any additional questions or need support, please get in touch with our technical team, we are here to help!

📞 01633 244777

[1] S, A. and F, R. (no date) Hardness in drinking-water, its sources, its effects on humans and its household treatment, Journal of Chemistry and Applications. Available at: https://www.avensonline.org/fulltextarticles/JCAP-2380-5021-04-0009.html (Accessed: 08 January 2024).
[2] Wilkinson, J. et al. (1997) Major, minor and trace element composition of cloudwater and rainwater at plynlimon, Hydrology and Earth System Sciences. Available at: https://hess.copernicus.org/articles/1/557/1997/ (Accessed: 08 January 2024).
[3] Kirwan, K., Gaylard, A.P. and Lockerby, D.A. (no date) Surface contamination of cars: A review – sage journals, Surface contamination of cars: A review. Available at: https://journals.sagepub.com/doi/full/10.1177/0954407017695141 (Accessed: 08 January 2024).

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