This paper focuses on developing methods for both potential and actual evapotranspiration (ET) models for the data scarce conditions of the Eastern Arc Mountains catchment of Tanzania. For reliable estimation of the components of the hydrological cycle and plant water uptake, potential ET estimates are required, and for catchment water balance actual ET estimates are needed. These potential and actual ET estimates, however, depend on reliable and good quality data records. The study catchments in this work are characterised by general lack of reliable meteorological (MET) data, though good records of rainfall, flow and pan evaporation data do exist in a few places. In the study reported here the Penman-Monteith (P-M) estimates were found to be closer to the pan evaporation model in areas where reliable records of pan data exist. By comparison, estimates derived solely from temperature (i.e. the Standard Thornthwaite method), were a lot lower. Assuming the P-M estimates to be reliable, new temperature based regional equations were developed using data obtained from six climate stations. The study also presents simpler methods for estimating actual ET from catchments.