The Central Queensland University (CQU) and GBG Project Management are collaborating on on-site wastewater treatment and reuse designs and installations. A design problem encountered has been large variations in wastewater generation volumes during the course of a calendar year. Treatment systems that are under-sized are susceptible to hydraulic surges that may result in poor effluent treatment. During peak wastewater production times some sites have insufficient land application area for the treated effluent. This paper discusses a concept design for wastewater treatment and reuse for small islands and presents data for a caravan park that has large seasonal variations in wastewater generation volumes. The caravan park has primary treatment, a CQU designed self-contained recirculatory evapotranspiration channel, a sand and zeolite filter, and a disinfection process. Effluent that is not transpired is reused aboveground in the sapphire mining process. Microbiological assessment of the treated effluent at the caravan park showed log reductions in the numbers of faecal coliforms and the nutrients, BOD5, and pH were all within the licence requirements for the system. The concept design for islands involves installing reticulated sewerage lines and treating the houses in clusters with small-scale wastewater treatment systems. The treated effluent is provided for sub-surface irrigation on the island. The aim of the paper is to demonstrate that variations in wastewater generation can be handled by appropriately designed systems.