The climate is a large driver of how much groundwater is used. During droughts, groundwater extraction may increase to offset decreases in surface water availability – and conversely, in periods of high rainfall, demand for groundwater decreases. This allows groundwater sources to be replenished. 

The amount of groundwater used by all water users varies each year, but on average, it cannot exceed the extraction limits (i.e. the long-term average annual extraction limit or the Sustainable Diversion Limit). These are outlined in Water Sharing Plans for each water source, which also includes the rules for extraction.