There are several ways of preserving water covering technical, legal and cultural aspects. More recently, Rainwater Harvesting (RWH) has become one of the popular means of water-saving. A few studies on RWH system at place of worship have been undertaken; however, there has not been any detailed study in Australia. This research aims to explore how Islamic scripture can be used to promote water conservation among the Muslim community, specifically, this examines the feasibility of a RWH system at St Marys Islamic Centre, New South Wales, Australia where a RWH system is proposed to supplement mains water for regular uses such as washing, gardening, and socio-religious functions. Based on local daily rainfall data, a water balance model has been developed to estimate reliability of a RWH system at the proposed location. The preliminary result shows that for a 10 kL tank size, the average reliability of the proposed RWH system is 69% for 400 people. However, if the tank size increases, reliability also increases and therefore, higher tank size is needed at the proposed site. Finally, this result will be useful to understand the effects of Islamic motivation and RWH on water preservation. It is also expected that the outcomes of this research will promote water conservation in places of worship and community centres across Australia and other countries.