Tomatoes really don't need all that much water: Put two plants in and then water them with . . .
unsalted vegetable cooking water, unsalted pasta water, rinse water from hand-washed dishes and such. And don't forget to stick a bowl under the sink to catch any "waiting for hot/cold water to come" wastage. If you are strong, and really dedicated you can stick a 5 gallon bucket under the shower head and save all that warm-up water to water plants with as well. My husband has been getting up and letting our chickens out in the morning and he takes all the chicken water and duck bath water and waters other plants, trees, the compost pile. . .
If you have people over and they are drinking bottled water, don't forget any leftovers in bottles from that too. I usually have a ton of these after I have my whole family over.