For water dont just pour water into whatever you are keeping him in or else he will drown.. You can get these things called water crystals and soak them in water or break off sponge pieces and soak them too. That's the cheapest way. As for feeding them everyone else seems to have given you the right answer. I had a friend who kept a cricket in his back pack at school and named it and he just fed it grass. He lived for a few weeks..
"Crickets are omnivorous scavengers who feed on organic materials, including decaying plant material, fungi, and some seedling plants. Crickets eat their own dead when there are no other sources of food available, and exhibit predatorial behavior upon weakened, crippled crickets.", according to Wikipedia.