I don't know if you have used this resource yet but awhile back the Canadian Guider came out with a special Water for Tomorrow edition. I know it was available at the White Oaks Area Guide shop. If you have a similar resource in Windsor you might want to try there.
When we did a water day we made each child a name tag made out of a water droplet and once the day was over it was a camp hat craft.
We also showed water moving up celery stalks with dye. That was really neat!
Have you thought about condensation? Perhaps boil a kettle hold a piece of glass or mirror over it and show the girls how it goes back into water.
You may also want to contact one of your Conservation Centres. They should have some good books and information packages.