This International Standard specifies methods for the determination of pore water pressure in both unsaturated and saturated soil using tensiometers. The methods are applicable for in situ pore water pressure measurements in the field, as well as for monitoring pore water pressure in, for example, plant Containers or soil cores used in experimental procedures. At normal atmospheric pressures, i.e. about 100 kPa, the application of these methods is limited to a range of pressures down to about - 85 kPa. The range is reduced at lower atmospheric pressures. Tensiometers will not function if sub-zero temperatures occur at the measurement depth. Their accuracy is influenced by seil and air temperature fluctuations. Tensiometer response time ranges from a few seconds to several days. To obtain reliable measurements under field conditions, tensiometers require frequent servicing. A tensiometer provides Point measurements of pore water pressure. To measure pore water pressure at different depths, several tensiometers will be necessary. In the field, replicate sets of instruments will be required if the spatial variability of the soil is to be allowed for