I want to use old auto windshield washer pumps (12 volt) to pump the water to the plants.
Clipper
I suspect that a auto windshield washer pump will not last very long. It is designed for a short duty cycle, to be run for short times only. Due to this it may heat up possibly burn out and/or the bushings on the motor shaft will ware out quickly. If you put it on a timer and ran it for a short time only it may last longer. It will be interesting to see how long one of these things will last, so you can tell others what to expect.
Later on if you need a 12 volt dc pump, you might try your local marine supply house. I saw some inexpensive submergible bulge pumps starting at about $10 and up. The $10 unit pumps 350 gal/hr and use a 1/2" hose. It looks like a 2-3" cylinder about 3-4" long. The higher priced units are again more longer lasting. A RV place may also have small 12 volt pumps.
All other kinds of pumps that I can think of (water cooler air-conditioning pumps, aquarium pumps, etc.) are 110 volt AC.
Mike
Thanks for the info Mike, I kind of figured a windshield washer pump would burn out as I am aware that they are designed for intermittent use. But, we need to know how long they last for information purposes. There are lot's of places where 12 volt pumps can be bought, but I am trying to figure out what may be just lying around for folks to get at easily. That would be the biggest purpose in the whole experiment. An experiment we can eat :-)
Clipper