If I put my hand in very hot water, sometimes my skin gets confused and it feels as though I've dipped my hand in cold water.

Why does this happen, and at/after what temperature does this occur?

As the origins of life and the eye are ocean-based, it makes sense that the properties of the human eye ("why we see what we see") were largely evolved to perform specific tasks suitable for water. The fact that we can only observe a limited range of the electromagnetic spectrum—the part that water doesn't filter out—being a good example.

However, is the fact that we perceive water as being "clear" important? Is our optic system calibrated to see clean water as "clear". Obviously there are many things to factor in here: what the eye receives, how the brain perceives colour, even how we sociologically define colours, but water having "no colour" and not causing alarm or distress, for whatever reason would seem to be a good default for the whole thing.

Does anyone have any thoughts on this?

If a glass of freshly-poured tap water is left to stand for a while, bubbles begin to appear under the surface of the glass. The bubbles do not seem to rise, and will remain there until the glass is drained. What causes these bubbles?

A gecko sticks to a vertical surface because of the huge surface area on its feet (thanks to microscopic hairs). If you ran the gecko's feet under a tap, (or dipped it in a pond), would the gecko just slide down/fall off the vertical surface, because it's feet were busy sticking to water molecules instead?

And if it did, would it have the emotional capacity or facial muscles to look surprised? 

I've always wondered if, with enough pressure, it were possible to compress water into a solid shape, and have it remain that way.

Some time ago I was riding old bicycle when the chain broke. I managed to roll 10 kilometres (150 metres down) on a former railroad trail so I got almost to my point of destination without having to get off and push. But it was very slow. I think the weight of my bag helped me. There were tools in it (unfortunately, none to repair a chain) but also 1,5 litres of water and some apples and sandwiches. I was afraid to comsume any during the rolling part not only because I was unwilling to stop the mostion but also because I thought it might reduce the weight. Would it? There was no toilet on the way, so the question is: wuold my body have breathed out more CO2 and breathed and sweated out more water if it had got more? I was not critically hungry or thirsty at that time, just a bit.

My local authority parks department proudly boasts that it uses recycled water, but isn't all water recycled?  Isn't there a finite amount of water on Earth and, if so, how often is each "piece" reused in human activity such as drinking, cooking, washing, agriculture and industry?

I also wondered if there was a ratio for this - in other words size of projectile and height of plume?