The path from seed to table is a wet one. Plants take a fair amount of water to grow. And if your harvest comes with as many little insect friends as mine does, you'll spend a while at the sink each night, washing the little critters and their poop off your salad.
Now, like most people who grew up during the California drought years, I feel guilty "wasting" water. And while I don't exactly consider watering my garden (or washing bug poop off my salad) a "waste," I do try to be efficient. Until I get around to converting the sidewalk-spraying sprinklers into a drip irrigation system, I'm watering by hand, and only when the plants need it. Now that the soil is warming up, I'll be applying mulch to prevent evaporation. And way up high on my to-do list is setting up a greywater system.
In the meantime, there's greenwater - the water I use to rinse off my harvest, hands, and trowels after gardening. It's real simple: I've got a big basin (actually a large metal Ikea planter without a hole in it) set up underneath an outdoor faucet. I rinse everything off there, the water sits in the basin overnight, and the next day I use it to water the garden.
The water stays in the basin less than 24 hours -- long enough to drown most of the pests I was washing off the plants in the first place, but not long enough to breed mosquitoes or bacteria. And unlike greywater, which generally contains some soap, salts, sweat, grime, bacteria, and other stuff that's fine to water ornamentals and fruit trees with but not recommended for things like lettuce, greenwater is fine for my thirsty little seedlings.