Just picked up a '78 240D from the central valley in California. The tap water there is very hard and the car got sprayed by a sprinkler system. The PO let it sit in the sun rather than dealing with it immediately.
I've done some internet searches and tried vinegar w/ distilled water as well as a couple of Meguire's products. Nothing worked so I stopped by a reputable auto body shop for advice. The guy said that they were the worst spots he's ever seen and that color sanding was my only hope. He won't touch the job however since it's a 30 year old paint job.
A friend recommended 3M heavy duty rubbing compound. Anyone have any ideas? Thanks,

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'81 300SD

Probably will have to resort to polishing>compounding>wet-sanding depending on the level of damage to the paint. I would say if you're not familiar with any of those techniques, to get a professional detailer to look at it and asses the damage. Forget about professional body-man, many of them aren't detailers (individuals that restore original finishes without painting) and are only experienced in refinishing techniques.

Definitely forget about the 3M stuff... way too abrasive.

I would polish it and then go over it with a clay bar. And last but not least a couple good coats of paint sealer and wax.

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current vehicles:
'82 240D - 125k - daily driver
'85 380SE - 299k - on dry dock
'87 Vanagon - 183k - sold

The problem is that the deposits are usually harder than the paint, so buffing will remove more paint than deposits.

Wet-sanding might be an option, but attacking it with a mild acid (such as vinegar) is probably going to be the least damaging. I'd even consider something stronger such as Tile-X or other acidic product, just try it on paint where it won't be seen first, and DON'T LEAVE IT ON!!! Rinse thoroughly and often if you find an acid that will work.

The darker the color, the more likely that the acid will make the paint blush.

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Gone to the dark side

- Jeff

Why use clay AFTER polishing?? Do you even know how a clay bar works, and what it's used for? It should be about the first thing you do after washing and drying the car...

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

My dad is a professional detailer and for water spots as you describe my suggestion would be acid.

I don't know where he buys it from (it's from a supplier) but I'll ask him tomorrow. What you would do is spray acid on a wet car (in the shade and do this in sections) and then rinse after about 15 to 20 seconds, you don't want the acid to stain the paint.. AND BE VERY CAREFUL WITH IT ON WINDOWS! Only do windows is the glass if cold and in the shade... You don't want to etch the glass. Acid is some crazy stuff, but I think it will do wonders for you and definitely get these spots off..

Again I'll ask him where he gets the acid from. Also as a quickie try steel wool on the windows (fine steel wool) it might take the spots off and if not make it easier for the acid.

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2007 BMW 328XI

You don't have to wash the car first and then clay, you can clay then wash the car... We use windows cleaner (when it's too hot to have the car sit in direct sunlight wet) on the area and then clay it.. Then wash the car, buff and wax... Comes out beautiful and the paint is smooth as glass

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2007 BMW 328XI

i have this problem with the single stage on my SD. The water literaly etches the paint, which is why you can see it only from certain angles in certain light (thats how mine is). I had to wet sand below the spots. I wet sanded with 1500, then 2000, then polish. Looks better now than when I had it painted.

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1981 300SD 512k OM603

Buffing won't even take them off, but make them shinier! LOL

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2007 BMW 328XI

I rented a house once that had the same problem on some huge windows in the living room, it drove me crazy. It was really bad. Near the bottom you could barely see anything through it. Utah water spots pretty bad too. When the old man who lived across the street saw me out front trying to clean the windows, he came over to tell me I was wasting my time, that others had tried, and they are permanently etched into the glass.

That made me all the more determined. I finally got it all off without damaging the windows. They glistened, there was no etching. I tried vinegar. (First I tried CLR, & got nowhere.) Then I tried no-scratch comet cleanser. I alternated between Comet and Vinegar, about 10 or so times each, until finally, there was nothing left. (Since the deposits were thinner near the top of the window, it was easy to tell I was making progress.)

There is bleach in the cleanser. You don't want to mix bleach and vinegar, so you need to rinse between each. Even after rinsing there is a slight amount of residual chlorine left from the cleanser. It seemed to react with the vinegar, actually foamed a bit. So when you rinse, you don't want to be 100% thorough. That seemed to be the trick. More deposits were coming loose with this technique than the CLR, vinegar alone, or comet cleanser alone.


I just remembered a new favorite product I've discovered since moving back to Utah. It's called "Shower Power". I'd tried it before, and wasn't impressed. Then one day, I read the directions.

It's very, extremely mild. It works by siting on the mineral deposits and breaks the molecular bonds. You spray it on, then do nothing. Seriously, don't even touch it till it's completely dry!

Come back after its dry and rinse the loose powder away. Repeat as necessary. It's basically doing the same thing as vinegar, but it's even milder. It works best when the mineral deposits are dry, when you apply it. (Probably because it's less diluted.) The beauty of this product is, you don't have to scrub hard or use abrasives, and it's very gentle. (It won't even hurt your skin) I've used it on gold plated bathroom fixtures, Italian tile, porcelain, and china. Some of my newer faucets are brushed nickle with a clear coat, and it hasn't damaged the finish on them, one bit. You get it at home depot. I'd try this before, the vinegar/cleanser method. You actually don't have to scrub at all. You might be tempted, but don't!

I can imagine that using any method that requires hard rubbing, or polishing is going to be extremely harsh on your paint.

In my experience, the solid paint colors are very forgiving, because they're nice and thick. If you have 30 year old metallic paint, the clear coat is probably very thin and weak. Your paint may not come through it, no matter how gentle your methods.

*Disclaimer: I am a Realtor, not a car detailer.

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1979 240D, 4spd manual, Power Sunroof, manual windows, 147k miles, Pastel gray/Black MB Tex.
1991 300D 2.5 - Smokes like it's on Crack!

"breaks the molecular bonds". That's essentially describing acid, which is a low pH (missing hydrogen), reacting with a basic such as lime, "stealing" the hydrogen atoms from the lime will break down the lime (rock). Same with calcium et al.

Provided that the acid isn't strong enough to damage the paint, and that there isn't wax protecting the deposits, this will work. Can take time. Beware that (soda) automotive glass is also basic, so prolonged contact with acids can leave surface pitting/etching.

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Gone to the dark side

- Jeff

The SDL has this problem too.. its really bad on the hood

Rubbing compound will probably strip the paint. Patience and mild cleaners will probably be less invasive.

I got good results on newer paint and "texas pinstripes" using Meguiar's Clear Coat body scrub to get rid of scratches in the clear coat. It's a mild abrasive cleanser.

You might try a household Heloise trick of soaking a paper towel with vinegar (or vinegar-water solution) and letting the saturated towel adhere to the side of the car. That keeps the mild acid in contact with the hard-water stained surface longer so a less harsh chemical can work over a longer period. Keep the towel moist with a spray bottle, if needed. That's a recommendation for cleaning bathrooms, not 30 year-old car paint, though. It worked in my shower where Lime-Away wouldn't and abrasive cleansers required too much effort or would scratch the surfaces.

Thanks guys,

I'll stop by Home Depot and pick up some Shower Power since that seems to be pretty mild. Babymog, you mentioned the presence of wax in your last post. The car had been waxed the day before it got sprayed by the sprinkler. What should I use to remove the wax before applying shower power?
Also, I've been using steel wool on the windows with a little success. Ajax and a plastic scrub pad have given me better results. The windows still aren't clear. What a nightmare.

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'81 300SD

I use either chrome polish or toothpaste on the glass.Paint I get a cleaner type wax.Then wax after that.Sweetwater Texas,and Tennessee are the worst places to wash cars.Followed by wells.Key is to dry cars fast.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran