4-20mA signals are standard for industrial applications. I believe you will need to read voltage so you will need a resister across the output sized to give you the required voltage drop across the resistor. If you used 250ohms it would give you a 1v to 5v signal.
I just ordered an Arduino pro mini, plan on connecting to my flow meter to read the pulses and report back to a raspberry pi that will log water flows for each zone, graph etc etc.. or Ray will beat me and add flow to open sprinkler.
The flow meter I have is:
http://www.nymet.com.au/valves/1flowsensor.html
was quite cheap on ebay! 🙂 🙂 🙂