I noticed there were a few looking for lesson plans in measuring with water. I don't claim to be the worlds greatest lesson planner but I find that using a little bit of history a long with a lesson can be kind of fun as well as a learning experience.
For measuring with water I am assuming you are looking for the volume of an object. Mr. I. Newton seemed to have discovered quite a neat thing about volume. He use to fill his bath tub with water to take a bath, all the way to the top! Jumping into the bath he noticed that quite a lot of water poured out of the tub. Heavens to Betsy, Volume of a human! Well, the idea is not as formal as i would like for it to be, (I have it written down in my notebook), but I just happen to run across a request.
Use something that you know what the volume is, (i.e., an aquarium), measure the amount of water that you have in it. Place an object in it, any old object, measure the water now. take the volume of the aquarium with the object, and without, voila'.
I hope it helps.