I had learned my lesson years ago, but got bit the other day by parking in an area where the underground sprinkler system sprayed out on my car.
If any of you have had this happen, it typically leaves some nasty hardwater spots that are tough as nails to get out (light color cars hide them better).
Honestly, having a car keyed and scratched might be eaiser than some of these spots to repair the finish.
I have been using Mcguires scratch X, Step 1 Paint cleaner, Step 2 Polish, and still some remain on the surface.
They are much more visiable on chrome surfaces. I will need chrome cleaner for that.

Anyone experience this? Have tips/tricks for removal? Recommend any other products?

They are a complete bitch to get off of darker colored vehicles.

Watch where you park!

Depending on the chemical makeup of the water there might have been acidic compounds in it that actually etched into the clearcoat. Especially if they were magnified by the sun.

You may need to go to a mild polish with a machine buffer to actually get them out (Porter Cable 7336/7224 for example)

The trick is to start on one in a small, inconspicuous spot and see just how far you have to go to remove it.

The well water around here has more iron than the Brooklyn Bridge - I have to move my cars next door when I water the lawn. I know from where you are coming, my friend... :(

if the Meguiars cleaner you are using is in a red bottle forget it, its watered down and will never work, at the vary least try my paint cleaner on my web site, like Jim says, you may need a da buffer or maybe even the high speed. last case effort is wet sanding which I don't recommend if you don't have experience. Gary

i experienced this same problem on a 67 mustang that was parked in a warehouse and the sprikler system came on from a fire or something. anyway it had factory paint and we didn't want to screw it up by using all kinds of harsh chemicals.

the secret weapon.....LIME AWAY. use a mild solution of it. worked extremely well without damaging the paint at all.

good luck

I've used a clay bar with distilled vinegar and received great results.