I love using water in photo shoots. It can be a a difficult element to use because you don't often get more than one shot at it. Water elements are best when done at the end of a shoot so they don't ruin the rest of your pictures with water spots on clothes.
Water makes a great backdrop or foreground, even if your subjects never get in the water. I love shooting by water, using its reflective surface to capture another image of the subjects.
If you have really adventurous subjects, you can have them climb straight into the water. If they are a little wary of that idea, have them roll up their pants and just barely wade in.
Water doesn't work for every shoot, but for summer shots it can be the perfect added element.