tx,

The first thing in designing any system is to know you demand for water. That is amount of water per time. So, to have your veggies survive, what kind of water is needed per time to do so? If water is limited to the capacity of your barrels (not supplemented with house water) and 24 hours a day to water, then your limit factor is capacity of barrels. For example, if you need 1/2 gal every two days per veggie plant; for 4 plants you need 2 gallons every 2 days (plants need varying amount of water thru their life cycle in relation to their root ball size). therefore a 55-gallon drum would last about a week without rain or supplemental water. You now can see how this goes. Mosquitoes are an issue if the water sits for more than 7 days. You need to raise the barrels higher than your garden substantially to get even low pressure for an auto system to work. The best delivery system I have seen and used is a pvc pipe with 1/16" holes drilled for delivery to buckets of vegetables. There are low pressure systems but very few. Google Earthtainers or look on the container forum for these.