Stains on the windows

Hello, I think you could try to remove with products that contains bleach.

Are you sure they're stains? Pure water does tend to be slightly acidic after exposure to atmosphere. There's a famous incident that occurred in my childhood where a scientist called he had discovered a new form of water, calling it polymerized water. Later, he found out that his glass beakers had been etched by his "pure" water and there were molecules of silica floating around in his water samples.

TTFN (ta ta for now)
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In my experience, these crystals are very difficult to remove the spots. I have gone through the same situation using various cleaning products without success.