These systems are interconnected,
with ground water emerging as springs to supply rivers and rivers
flowing into the ground water. Some experts believe 91 percent
of the liquid freshwater on earth is in great reservoirs in the
rocks. Flat plains, formed by ancient river systems often contain
large underground aquifers fed by runoff from adjacent mountains
and slow-moving rivers. The great bulk of the groundwater, however,
is believed to be ancient and either non-renewable or very slowly
renewable. Extensive groundwater use in other areas of the world
has led to subsidence of the ground and permanent draw-down of
the water table.
Surface waters respond quickly to droughts or heavy rains, but groundwater tends to remain stable, longer. In recent years, New Zealand was subject to record breaking droughts followed by record breaking rains and floods. During floods, sewage and soil erosion contaminates the water supplies making them dangerous to drink. These uncertainties have increased the development of ground water supplies. In New Zealand, 37% of the water supplies now originate from ground water.
New Zealanders consume nearly 2,000 million cubic meters of water per year. Total water resources are estimated at 350,000 million cubic meters per year distributed unevenly over the islands and mountains. On the south island, high mountains create a significant rain shadow and rainfall of more than 10 meters per year have been measured in some areas of the mountains while less than 340mm of rain may fall in the rain shadow areas.
Agriculture uses more than half the water supply in New Zealand with 350 million cubic meters of water used for livestock. 1,100 million cubic meters of water are used for irrigation of pasture lands and crops. More than 234,000 hectares are now irrigated. The irrigation schemes have been largely funded by the Government. Most of the irrigation comes from surface rivers and used in inefficient open ditches to water livestock and grasslands. In 1992, only 160 km2 of New Zealand croplands were irrigated.
85 percent of the people live in urban and peri-urban settings. Cities require large quantitiesof water for human and industrial use. In Auckland, water use is about 380 litres per person per day. Of this, domestic use accounts for 51% of urban water resources (Auckland), with industry, commerce, recreation, and leakage equally sharing the remainder.
New Zealanders use 760 litres of water per family of four per day, 228 litres of which go straight down the toilet. Only 2% is used for drinking. 25% is used in the kitchen and laundry, 25% for other bathroom use, and 20% is used outdoors. Even more water is consumed indirectly. For example, a steak for dinner requires 13,250 litres of water to reach your table. An egg for breakfast takes 450 litres of water to arrive on your plate. The ton of steel in your car needed 250,000 litres of water to create.
Even minor efforts at water conservation can substantially reduce water use without creating hardships. You can save 200 litres of water per day, 1400 litres per week and 72,000 litres of water a year if you: