Testing the infiltration capacity of the soil is a specialist job. For the infiltration of rainwater or wastewater the infiltration capacity has to remain high. Using the right equipment this is fairly easy to determine. However, for storage dams, wastewater holding ponds and oil terminal linings the infiltration capacity has to be extremely low. Measurements of infiltration well below the evaporation rate is much more difficult. Also the lateral capillary spreading has to be accounted for. This can be done with a dual ring infiltrometer. When in clays the infiltration may only stabilise after several hours or days: an automatic filling device is indispensable (pictured).