Neat idea but the logistics are crazy.
Lots of water
lots of electricity
A pain to get the water to the dump station. ( multiple trips using your waste tanks)
You'll need chemicals to keep it sanitary. Too little and bacteria grows giving you a rash. Too much and you can get a chemical burn.
The next family gets to look at a dead spot in the grass, some parks don't allow mats or even screen houses to protect the grass.
The last thing is safety and insurance. You can't be at the tub constantly so a fence will be needed to keep the kiddies out.