THE SUSTAINABILITY OF a groundwater-based farmer-managed irrigation system (GW FMIS) cannot be guaranteed, but if the necessary conditions are not provided its demise is assured. A groundwater-based water users association (GW WUA) will be unsustainable if it cannot raise sufficient funds and manage its money, if it cannot obtain quality maintenance and repair (M&R) services on site, if the necessary spares are not available, if the tubewell (1W) suffers frequent breakdowns in mid-season, or if the energy supply is unreliable. Subsidized financing of M&R by the government is in the long run detrimental to the WUA as they are unsustainable. Eventually government priorities change. Provision of these services by the government prevents the spread of expertise and the development of a market for M&R services. Thus there is no backup source when the government ceases to provide them. This paper describes the concept of sustainability, the approach for achieving it and the conditions necessary. Application of this approach is being tested in the Bhairawa-Lumbini area of Nepal.