Hard Water Spot Removal Techniques

Hard water is an issue for much of the USA, and here in the Rocky Mountains of Utah we have some hard water that creates some difficulty in the removal of spotting (I frequently see  180-220 ppms and please refer to the chart below).  Many people know that water spotting is unsightly and go to great lengths to prevent it and just plain avoid it………however sprinklers don’t care about your car.  If you are quick with cleaning up these spots while they are fresh they won’t get set into or on the paint.  Along with the minerals left behind on the paint, the water drops act like little magnifying glasses that “burn” the sun’s rays into the paint, this can cause deep etching.

When a water drop is deposited onto your car it carries with it a group of minerals;  Calcium (Ca++), Sodium (Na+), Potassium (K+), and Magnesium (Mg++). Calcium and Magnesium are the most common.  These minerals are in solution and cannot be easily seen until evaporation occurs. These minerals are then left behind (precipitate) as a mineral ring on the object.  The hardness of the water is a product of the amount of minerals within the water.  Any measurement above 15 ppm (mg/L) will leave spotting or the mineral precipitate.  If you don’t have a ppm meter call the local water softening supplier and they can give you numbers, sometimes they report in grains…..1 grain is 17ppm IIRC.


Classification hardness in mg/L hardness in mmol/L hardness in dGH/°dH
Soft 0–60 0–0.60 0–3.36
Moderately hard 61–120 0.61–1.20 3.42–6.72
Hard 121–180 1.21–1.80 6.78–10.08
Very hard ≥ 181 ≥ 1.81 ≥ 10.14


So what do you do if you have a car or any object that has water spots?  In detailing we often try the least aggressive method first in ALL THINGS. I don’t care if you read that I used xyz product with abc application, you don’t know what I did to get to that point and it’s likely it won’t work BEST for your situation.  ”You don’t need to use a sledge hammer to drive a nail”  Okay I’m climbing off my soapbox…….  I would mix up some White Vinegar (if you like apple scent use apple cider vinegar :) ) with distilled/filtered water in a 50/50 ratio, spray that onto the affected area and gently wipe.  Why does this work?  Vinegar is a weak acid and the water spots are basic (alkaline), so the acid will neutralize and break up the basic (alkaline) minerals.  So if the vinegar doesn’t work, increase the ratio of vinegar until you get to straight vinegar if necessary.  I have two bottles in my gear, one 50/50 and one 75/25 ready to go, its also good window cleaner.  If the vinegar doesn’t “cut” it then its time to step up the acid strength.  In a previous article I did on scum removal on a boat, the stronger acid I used on that gel coat has not been tested for automotive paints.  So I have searched around for a safer product for automotive paint.  I have been super pleased with the Chemical Guys Water Spot Remover, it works very quickly on tough spots that have sat for some time.  I’ve taken some photos to show you just how effective this product is. I literally just applied it to a terry towel (use MF for paint) and gently wiped it on in back and forth motions and wiped it off with a clean damp towel.  Wipe the area down with different clean sections of your damp cloth and don’t allow the remover to dry on the paint.  I tried to show in photos the effectiveness on paint but all my photos just didn’t do it justice……so I used it on the shower glass……bingo nice photos to show effectiveness.  You can also impress your significant other by cleaning the shower glass and earn some bonus points……….trust me I know!

Pretty thick coating of water spots



Another angle




Yes this bottle is on the other side of the glass




Nice clarity




Final shot




I have some experience that shows that wax will be removed, sealants are also mainly removed or greatly reduced, but that’s what they are suppose to do……a sacrificial layer of protection.  I like it and use it on my daily driver which has an Opti Coat or Opti Guard coating applied. I’ve had it on for over 2 years without reapplication, my friend Chad Raskovich at Raskys Auto Detailing shares a bunch of info about this product just click the hyperlink.  This coating takes the acid found in CG water spot remover incredibly well and it really protects against possible etching of the minerals into the paint.  This coating will take the beating and not your paint. If you have to polish to remove etching you will be removing the coating NOT the clear coat at first.  If you get aggressive you will start to work on the clear coat at that time.  I have had to use the spot remover on two occasions without ill effects in my experience.

The other suggestion is to use the CR Spotless filtered water system when you wash your cars. While this can’t help against the rouge sprinkler, it makes it super easy to dry the car as you don’t have to towel it afterwards.

Good luck in keeping your car spot free, and if you get spots I hope this helps.




Greg Nichols Reflections Detailing
Greg Nichols
Reflections Detailing
Logan, Utah