Guidelines for Very Low Pressure Drip Systems

Gravity flow systems tend to have extremely low water pressure which creates problems with emitter operation and a lack of watering uniformity. The first emitter on a tube will very likely put out a lot more water in 30 minutes than the last emitter will. Standard electric actuated irrigation valves will usually not work with these systems due to the low water pressure. To automate them you usually need a more expensive motor-operated valve. Fortunately most folks using rain barrels aren’t interested in anything fancy and just turn the drip system on and off using an old fashioned hand operated valve.

Flag Emitters
Typical Flag/Take-Apart Emitters, the one on the right is disassembled.
This is a short path emitter, but this brand was sold in a package incorrectly labeled as a “turbulent flow”.
The pen is to show the size of the emitters.

If you are planning to use a rain barrel or other low-pressure gravity flow system I recommend you try the emitters commonly called “Flag” or “Take-apart” Emitters.  You will find more information on these on the emitters page.

Elevate Your Rain Barrel!

Unless the water source (rain barrel in most cases) is elevated a meter (3 feet) or so above the emitters, even the low-pressure flag emitters may work poorly or not work at all. A barrel set on the ground often works well when the barrel is full of water and then stops working as the water level drops. The solution to this problem is to elevate the barrel on a stand. To get really good water distribution uniformity it is often necessary for the water source (barrel) to be 10,5 meters (yes, that’s 35 feet) above the emitters. Height creates water pressure, and the pressure is necessary for good uniformity. With that said, it is my experience that most people who use water barrels are more interested in having a primitive or “green” irrigation system than they are in having an efficient one, and are sufficiently satisfied with the uneven water distribution.  Keep your drip tubes as short as possible. I strongly recommend that you mock-up a test system using your barrel, a valve, filter and at least one row of tube with emitters and test how well it works. You can then make modifications as needed to your design before investing too much money on materials you might not need. Remember the key to success if you have problems is almost always to raise the height of the barrel. A lot of people give up without trying that simple solution!

Also please consider these related articles:

Automating a Rain Barrel Irrigation System

How Elevation Impacts Pressure in Irrigation Systems