I saw this idea here and decided to try it out. I bought the plastic drop cloth and duck tape at Walmart for under $10 for both. I bought the drop cloth that is in a 10' roll that rips off into ten 10' squares. I bought the teal duck tape because I thought it was cute.
Originally I was going to use food coloring like the blog said, but after I thought about how it was likely this thing would leak and I didn't want to ruin 3 kids' clothes by them splashing in food coloring water, I decided to leave the food coloring out of it. (Good call on my part.)
Despite that my husband didn't think this would work very well, it was a HUGE success! Everyone loved it, and what I planned on being an hour or two activity literally turned into an all day thing because it was such a big hit.
I started out by unrolling the tarp I bought and taping the perforated edges to prevent water from leaking at them. I made two 40' x 10' tarps, and folded them each in half to make two 20' by 10' double layered tarps. I double layered it because my tarps were about the thickness of garbage bags and I was a little skeptical they would hold up with 3 kids running and jumping on them. (Again, good call on my part.)
I put the 20' x 10' double-layered-tarps on top of each other, and rolled the edges and duck taped in place. I left a hole at one corner for the hose. This whole process took about 40 minutes.
Once taped I stuck the hose inside so there were 2 layers on bottom and 2 layers on top, and started to fill it up. I had the kids show me where the initial leaks were. We patched them up (there were only 1 or 2) and filled the whole thing up.
Things I learned while filling this up:
1. This thing works best on flat ground. If you start out on a hill, even a little one, one side will be far more full than the other.
2. Once this starts filling up you really can't move it without it tearing.
3. Once it's filled it's pretty sturdy. The kids can run, jump, roll, and slide on it and it holds up for a long while (a couple of hours) before it starts leaking enough they are really getting wet.
4. Before it's filled it isn't too sturdy. Their feet tended to get caught on the plastic and drag and stretch and tear it. I discovered this quickly and made them wait until it was filled to play on it.
5. You really don't need food coloring, in fact I wouldn't recommend it.
This could be the best outside toy I have discovered so far. They LOVED it. At first they didn't get wet at all, but the cold water kept them cool in the hot sun. I told them to go for it and play as rough as they wanted because it was there to have fun, and if it popped we could always turn it into a large slip-n-slide.
They would run across the yard and slide on it. They would roll and watch the ripples go all the way across what they called the "water bed".
After a couple of hours we started getting a few leaks. I didn't bother taping them up because they weren't too bad. The bag stayed full enough to be squishy and fun to run across the yard and jump on all day but after a few hours there was just enough water on top to make it splash as you ran or rolled across.
This picture (above) was taken after 6 or 7 hours of rough play on it. You can see where it is leaking and wet, but it still squishy and fun. Everybody loved it.
We paired this activity with lawn chairs, a couple of rounds of popsicles, a kiddie pool, and a water gun fight.
I heard the boys say multiple times that this was the best day ever, and one of the funnest things they have ever done.