This is a term used, but not defined by the National Water Act. It relates to the size of the water resource rather than its importance. A resource is deemed to be significant if it is large enough to warrant it’s own Reserve determination.
Why are significant water resources important?
Reserve determinations are required for significant water resources and they need to be protected, used, developed, conserved, managed and controlled.
Source: http://www.randwater.co.za: Vaal Dam