You may have cold water spray

The instructions are confusing, especially when unused to Japanese toilets, but the use of 'may' struck me above all. It is clearly used for a possibility here- of something to be avoided, but the concept of permission/positive possibility does shine through. I can't help wondering whether the teaching of the form has led to this sort of mistake. Would it make more sense to teach forms that could be used with fewer problems rather than forms native speakers use?