Double-Ring Infiltration Testing is performed in a very similar method to the Single-Ring test. However, two pipes are used concentrically. The outside pipe should be roughly 3x the diameter of the inside pipe. Both rings should be filled with water, with both water levels recorded regularly and both levels kept roughly the same during the test. The purpose of the outside ring is to reduce the impact of lateral water flow from the interior pipe. The data from the interior pipe is used to determine the infiltration rate.