The can test uses an array of containers to measure how much water an overhead sprinkler system delivers. It can be used to discover two different things: how much water a sprinkler system delivers in a set amount of time, and how even the pattern of the sprinkler system is.
The test is quite simple. A pattern of small cans is set out on the lawn or garden area, and the sprinkler is turned on for a set time, then the water in each can is measured.
The cans must be straight-sided, but they don’t need to be the same size. Tin cans, milk cartons, or any straight-sided (not tapered) plastic container will work.
Place the containers in an array that will answer the question you are asking. If you are testing how evenly your underground sprinkler system delivers water, spread the cans evenly across the lawn. If you want to know how much to overlap settings on a hose-end sprinkler, place a row of cans from the sprinkler head to the farthest reach of the water. If you know that a sprinkler system is well balanced (delivering water fairly evenly), and want to know how much water it delivers in a set time, just a few cans will suffice. You will measure the water in each and find the average for your answer.
Run the sprinkler for a set period of time, then measure the depth of water in each can with a ruler. Record the depth as you measure. Because you are recording the depth, the diameter of the can makes no difference, nor does the height.
If you are testing distribution, the difference in the depth in cans gives you a clear picture of the pattern of the system. Adjust the system to try to get the same depth in each can.
If you are testing precipitation rate, average the depth in each can to find the average rate for the system, or use the can with the least water as the standard.
To fine-tune a sprinkler system, use the can test to adjust the system as evenly as possible, then set the time the system is on to deliver the amount of water you want to the area that is getting the least water.