WATER

The simple rule with water is "the more the better" I use a 5 litre bucket for most of my painting. If I am working on oversize paper I use a 10 litre bucket. Try to avoid using a tiny little container unless you are painting on location.
Unless I'm doing a high key wash with a saturated colour, I don't worry too much about having clean water. The odd occasion when a pure clear wash is needed, I spray some water into an empty well on the palette, spray the brush clean and mix the wash there.

WATER SPRAY

Probably one of the cheapest pieces of equipment you will buy! Find one that sprays a really fine mist. They're great for softening ink lines - a quick, light spray while the ink's still wet.

They are also handy for wetting paper and gum tape when stretching watercolour paper.