I suppose you could use storm water to charge or make a spell much stronger, since you wanted to use it because of the strength. But they can also be used for curses as Voo stated.
An example would be to use the water for a spell. Let's say it's for a banishing spell.
This spell is just an example, but also something you could maybe try in real life if you wish.
Get a small mason jar, your storm water, some sage and salt.
This is optional, but you'll want to bless your storm water of anything nasty. You then can pour the water in the jar and put some sage and salt in there. Maybe you could set it on the windowsill or coffee table as a little sea-themed decoration?