This paper describes a new instrument designed to measure cloud or fog total water content mounted on a tethered balloon facility. The instrument is an evaporator type, which is inexpensive and relatively easy to construct. The device measures total water content with an uncertainty of 0.3 g kg–1, and a resolution of 0.03 g kg−1, at a frequency of 1 Hz. This typically gives a spatial resolution of 5–20 m and allows turbulent statistics to be calculated. Tethered balloons provide an ideal platform for the instrument to study low cloud, allowing very detailed measurement of cloud structure to be made. Some typical data are presented as an illustration.