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I dunno if you have anything to worry about i've never done water ramps before, but if you are worried either get a cheap liner, or head to a used sports store and grab a super old pair of boots. Both options are pretty cheap.
If i were you though i'd be more worried about your skis snapping, i here that happens frequently.
to all people scared of equipment damage i went to water ramps two years in a row and ur boots dont get ruined, snow is water too, but still getting ur boots wet doesnt harm them just let them dry. skis breaking IS rare, so dont worry about it.