For some people going to the pool is not an option. There may not be a pool close or it may cost to much if you have a big family. So you can create your own water day at home that will be a memorable experience. Here is what you can do.
Save ketshcup bottle that are plastic and rinse them out well. These will be used for squirting. Buy a few inexpensive squirt bottles as well. A package of water balloons costs about a dollar as well. Fill them up and add them to a bucket that has water in it.
Old margarine containers work great at throwing water as well. Have plenty of small and large containers available.
Fill a pool up as well if you have one on hand. Then set up your area. Keep a hose handy so you can refill the pool if needed. Grab yoru suits and start throwing water balloons and pails of water at eachother. THis is so much fun.