Just guessing, but the deposits look like hard water calcium deposits, but the dark spots look like mold growth started in a few places as well. Perhaps your water hose still contained enough water to drain into the storage bucket (if hose was open ended) and with time, warmth and moisture, you have the resulting various deposits forming. I assume the bucket had a lid from your description, which does not allow any moisture inside to evaporate quickly. Also if you have not used the coach for a while it would be wise to treat your fresh water system and water hose to a complete sanitization fill and flush to make sure all lines and tank are cleaned of any bacteria that may have started growing.
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