In many parts of New Zealand, the rocks at shallow depth (< 1 km) have high porosity and may contain up to 30% (by volume) of water. Usually, the pores and fractures are connected so that the water in the rock can move in response to pressure changes. Fractures have high permeability and allow water to move quickly from place to place. The Resource Management Act (1991) differentiates between geothermal water and cold groundwater on the basis of temperature: water greater than 30C is geothermal, that below 30C is groundwater. This distinction has no scientific foundation–it is based solely on the concept that water above this arbitrary temperature is an energy resource–it is not possible to clearly separate geothermal water from cold groundwater on the basis of temperature alone