How long can plants last without water (read more)?

I was growing beans, cubers and tomatoes in dixie cups and pots in my kitchen. When they started to attract ants I moved the pots and dixie cups outside. Due to my heavy school and work schedule I don't always get a chance to water them. I'm lucky if I get to water them every other day. Because I live in California the water sometimes dries up very quickly by the afternoon. When I went to go water them this morning some of my tomatoes appeared to wilt. I had watered them 2 days earlier. How long can plants last without water?