info from:http://www.drbeasleys.com/blog/2013/03/20/how-to-avoid-quickly-remove-waterspots/

How To Avoid & Quickly Remove Waterspots

Spring brings rain and with it waterspots. So as not to fear the forecast, there are two ways you can protect yourself against the inevitable evaporation of rain on your (ideally) spotless car. Continue reading and see how two simple tips can keep you looking great even if the rain comes down.

1. Seal your car and add a layer of wax.

By seal I, of course, mean use a paint sealant to shield your car from the affects of poor weather. Then, once you’ve allowed the sealant to cure (unless you use an instant bonding paint sealant), layer up with carnauba to increase shine, resilience, and the ability to repel precipitation. Not only will your paint be protected against UVs and damage from environmental fallout, but you’ll have rain beading up and running off your car like it was greased in oil.
The slick surface won’t allow water to sit still and, therefore, it will not be able to dry and cause spotting. In addition to this, you can quickly wick water from flat surfaces with a microfiber towel and have no problem at all.

2. Utilize a detail spray on a regular basis.

While it might be tempting bust out the bucket and grit guard and do a full wash when you get waterspots, it may not be necessary. If you’ve let the blemishes sit on the paint surface for quite some time then you may need to wash the car (or maybe even use a paint cleaner). But if they’re relatively fresh there’s no reason you shouldn’t be able to wipe them up with some touch up spray and a microfiber towel.
There’s no fighting spring showers, but you can certainly avoid the unsightly remnants left behind from a quick-drying rain. Protect your finish and stay prepared with a detail spray and you’ll be set regardless of adverse conditions.