Standpipe piezometers are often used in wetland hydrologic studies for measuring pore-water pressures and, therefore, hydraulic heads. Here, we consider the errors associated with the use of simple standpipe piezometers in wetland soils. The performance of two typical piezometer designs was assessed. Rather than measure the performance of the piezometer designs in the field, we modelled their response to computer-generated changes in pore-water pressures for three ‘model’ floodplain soils. We showed that for some piezometer design/soil-type combinations, standpipe piezometers can be in considerable error. Greatest errors were found where the less efficient of the two piezometer designs (standpipe inside diameter = 5 cm, outside diameter of intake = 5.6 cm, intake length = 5 cm) was in a poorly permeable silt deposit (hydraulic conductivity = 6 cm d⁻¹) overlain by a permeable sand (hydraulic conductivity = 210 cm d⁻¹). If undetected, these errors could lead wetland researchers and/or consultants to make erroneous conclusions about both patterns and rates of ground-water flow in wetland soils. In field investigations, we recommend that selective use is made of rapidly responding piezometers, such as closed hydraulic piezometers, so that the performance of standpipe piezometers can be assessed.