Water Spirits, offerings? Options

Is there anything typically found to be used as an offering to water elementals? Something to appease them in asking for their help, or something. Most of what I've read says that various incenses are the most common offerings to misc. spirits, but I somehow don't see burning smoke as the best option for water dwellers... any ideas? :S Thanks a lot.

Elemental kings and such like actual offerings, but most pure elementals seem to like you to do something for their element. Gnomes like you to plant something etc. Offer to clean up a local creek or river, then go pick up trash along the banks.