How about water? (IMG:
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I'm not joking, LOL. Seriously, herbs that relate to water might work well too. Get an earthen bowl for example, or glass, get rain water o stream water (bottled water will do if you can't get those things), put some herbs in there that relate to water (don't look at correspondences, look in agrippa book 1), and offer that. Simple (IMG:
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Whatever you do though, be extremely respectful. Don't demand anything, don't be rude. Otherwise you might end up with years of bad plumbing and other horror stories to tell your grandchildren about, LOL.