To make a water slide you need a slope with enough gradient to make you slide easilly but not enough gradient to reach dangerous speeds and have problems stopping. Here we use two colums of straw on either side of the run. On top of this we placed a lot of cardboard from IKEA furniture onto the straw to protect the sliders from stones. The cardboard was then wetted.
We found some bubble wrap and some black plastic which is normally used for planting crops through. We had continuous supply of water running down the slide and washing up liquid was added to further reduce the friction.
There are many different techniques for using the water slide. The best method was using a piece of plastic under the body because the contact of clothing on plastic generates friction. The best speeds were attained by going on the back and then leaning back. It also helps if your friends give you a push at the start.
It would be better to have a steeper slope for the forward diving position.
Making and using a water slide can provide endless hours of fun and hilarity.