Add Blue questions.

I just commented on the Add Blue needed on our new Tin Can and seems more of us are required to buy the stuff at an incredible price for what it consists of.
Basically distilled water and ****. If so it's a remarkable con in more plastic containers polluting up the planet?

I find it amazing that the engine will stop if not topped up with this Add Blue. OK we get warnings although I have no idea how big the tank is or how much is in it.
Is it possible to dilute it will more distilled water? How much accuracy is recorded? Does it really do anything beneficial for our environment?

After seeing it advertised online from €18 to €58 a container, we came across it in the local and not so cheap supermarket at €12.99 for 5L.

Ray.