That the ‘water supply system’ is sustainable, technically and institutionally and indefinitely - most importantly that eventual replacement or expansion of the system can be delivered within the existing framework.
That the system is equitable and covers the entire population- a system that reliably and sustainably meets the needs of 80% of the population while leaving the poorest 20% unserved cannot be counted a success.
That the resource is sustainable - that is that the system does not fail at any time due to failure of the resource - e.g. due to drought, excessive water table draw-down, streams drying up etc.
