I work with glass a great amount and always recommend using distilled or bottled water to ensure your not introducing any more salts or minerals than are already there.

Never wipe or rub the filter with a cloth, without first soaking or at least rinsing the filter with fresh water, I normally use fresh warm water if available and a can of air to blow dry the filter.

I shoot in Yellowstone national park alot, and the geysers are heavy with minerals, I always carry plastic containers with me that I can fill with distilled water and soak the filter in case of contanimation, I then rinse and blow off with canned air and then let air dry.

One of the biggest problems with wiping filters that have been sprayed is you will drive the minerals into the filter ring, which can cause corrosion to form under the ring, and you will almost always scratch the coating. I also use a very mild dish soap, as we do with our ground glass screen to help 'float' the contamination away.

Dave Parker
Satin Snow Ground Glass