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I have a 200 litre water butt and plenty of 22 mm plumbing pipe and fittings and I want to build an irrigation system for my vegetable patch so that I can open the tap after a few dry days and ensure all my plants get equal amounts of water from the butt.

The end of the patch is about 5 m from the water butt and at the same level, so the head is only the depth of the water-butt (1 m) plus about 10 cm as it sits on a small platform I built. I will bury a hose 20-30 cm under the ground to the end of the vegetable patch, where it will come back up to the surface and split into 4 rows of pipe about 15 m long each with holes drilled to release the water.

I think I should taper the holes so that the ones at the start will be smaller and the ones at the far end will be bigger, but given the low pressure I don't know how small these should be or what the size-difference in holes I should use from one end to the other to ensure that water gets all the way along and is evenly distributed?

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Controlling the pressure with variously sized holes will be a fairly difficult task. It may be simpler to run hose with no perforations along the length of the planter, and then place the hoses with perforations as branches off of your main line. That still won't lead to a perfect distribution, but would help. Another common approach to this is to use so called 'drip emitters' which are very cheap regulated orifices. They are designed to put out a certain volume per time, relatively independent of the pressure. I don't know if they can be buried.

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  • $\begingroup$ Yes, the drip emitters can be buried. I've done so with many projects. It gets frustrating when you have to repair the line though... :-) $\endgroup$
    – user16
    Jan 26, 2015 at 15:22
  • $\begingroup$ We use to have a lawn watering hose that was flat, with three or four little holes, every few inches. (Spraying this way and that.) You would notice more flow rate for holes near the inlet at low pressure/ flow rate. But at high pressure it seemed like all the streams were about the same. (I'd go down to the garden store and ask someone there.) $\endgroup$
    – George Herold
    Jan 27, 2015 at 3:44
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A second option would be simply to have a small container that you fill up and cap (like a bucket with an airtight lid). Then distribute your piping with perforations at will. Arrange your system so the bucket is elevated enough that the soil can swap the water for gas (like a do-it-yourself water tank system):

Aqua Globe Diagram

So long as you make the cap on the tank airtight, water can only leave when the soil emits gas to displace the water in the tank. Then you just fill the bucket up, cap the lid, and allow the water to dispense when the plants need it.

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