hog,

A small submersible pump might be what you are looking for or a transfer pump outside your barrels. What flow and pressure would you need. Aloha

Lehua,
I was thinking 25-30gph, and probably around 15-20 psi for drip irrigation ??

Here is a 12v model that might do the trick, it's a diaphragm pump though and I'm guessing you'd prefer 110v instead - http://www.grainger.com/Grainger/FLOJET-Potable-Water-Supply-Pump-2XE90

I am unaccustomed to dealing with pumps that small except for metering fluids, many metering pumps are much more expensive than the one in the link above.

A small peristaltic ("squeeze") pump may fit the bill though the price could be out of reach. I've used several diaphragm pumps for metering bleach and polyphosphates over the years and have found them to be troublesome, they have all been replaced with peristaltic pumps.

hog,

First design how many emitter heads you need and what the flow rate will be for the heads. Add that up and see what your gpm or gph rate you will need. Also decide how long you want a zone to irrigate. Your gph will decide how long it will take to irrigate. Also calculate time and rate to get volume of water needed per irrigation cycle per zone. compare that with your storage capacity and see how long your storage will last. In other words, start with your needs and work backward to design your distribution and then your storage amount. Aloha