I recommend that you watch the measured Irrigation video:
Unpowered Measured Irrigation Controller
 
The Unpowered Evaporative Valve has been accepted for the Smart Approved WaterMark.
 
You can upgrade your drip irrigation system so that all your plants are irrigated automatically and you can leave your garden unattended for weeks on end. Measured irrigation is a new method of irrigation scheduling that responds to the prevailing weather conditions. This means that you use much less water without affecting the yield.
 
Working pressure 10 - 800 kPa.
Maximun flow rate 480 L/h at 100kPa.
Fully automatic.
No electricity is needed (no batteries, no solar panel, no solenoid, no computer).
It is a smart irrigation controller because the water usage (litres per week) is directly proportional to the net evaporation rate. 
You can adjust the water usage (litres per week)) by adjusting the control dripper. 
You can adjust the irrigation frequency by adjusting the float.
Can be used for both pressurised and gravity feed systems.
Can be used with pressure compensating and non pressure compensating drippers.
Can be used for sprinkler as well as drip irrigation,
The water usage is independent of the water supply pressure.
This incredible invention is very simple, easy to install and use.