Set some tuna cans out on your lawn (take the tuna out first). Use about eight cans for an average-size lawn, placing some at sprinkler heads and some in the spaces between heads. Run the system for exactly 15 minutes. Then use a ruler to measure how much water is in each can. If the water depth differs by more than 30 percent, change the sprinkler-head spacing to improve coverage; double-check your repair work; repeat the catch-can test; and measure the depth of water in each can. Add the depths, divide by the number of cans to get the average, and then multiply by 4 to get the precipitation rate in inches per hour. Use this figure to develop a watering schedule (see the next section).
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