Water is pretty plentiful where I live. We don't ever seem to run out. It is clean and it is free (unless you buy bottled water). Here's my answers to your questions:
1. My family doesn't harvest rain water but my next door neighbor does to water her plants in her yard. She uses a rain barrel.
2. We learned about conserving water at school but I don't really practice it at home too much. My sister always tells me to turn the water off when I brush my teeth though.
3. I don't live in a desert so I don't know much about this.
4. Our water is pure. Once after a really heavy rain storm though we did have to boil the water before we could use it.
What is the water like where you live?
Will