Try some white vinegar diluted 50-50 with water on a mineral-coated inconspicuous spot. If that takes it off, it should not mess up the clear coat or other sealants.
Water deposits are usually calcium based.
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Rich, KE4GNK/AE, Overkill Engineering Dept.
'The Silver HamShack' ('07 International 22FB CCD 75th Anniversary)
Multiple Yaesu Ham Radios inside and many antennae sprouting from roof, ProPride hitch, Prodigy P2 controller.
2012 shortbed CrewMax 4x4 Toyota Tacoma TV with more antennae on it.