What we do is take a tarp, some rocks , a hose , and some soap. Place the tarp down on a hill place heavy rocks on the corners, place the hose onto the tarp and every once In a while add some soap. This is so much fun the whole family loves it !
we have a 2 tarps and we put them together to make it extra long. we made a sprinkler with PVC pipe, like the picture. we go down it on soft sleds or boogie boards and use baby soap to make it really fast.