Save water by growing your own

Most of the fruit and vegetables that we eat have a water content of between 90 and 95 percent, so a continuous and uniform flow of water through the soil is essential.

The nutrients that the plants need are only available when they are dissolved in water, so water not only provides moisture but food as well. No matter how much organic matter is contained in a soil it only becomes ‘digestible’ to plant roots when it is in soluble form. Water is the lifeblood for plants.

The average Australian uses over 1 million litres of water each year – a tiny amount through the tap and a huge amount in the provision of food, power and consumer goods, which is called ‘embodied water’.

Of the one million litres of water consumed each year, 70% of that water is applied by farmers irrigating crops and pastures to grow our food (fruit, vegetables, meat and milk). Another 20% is used by coal-fired power plants and other industries to provide consumer goods. So 90% of our water use is embodied in the goods and food we buy. The amount we directly pay for washing and indoor use is about 6% and a further 4% for gardening. So far our governments have only applied restrictions to gardeners, ignoring the 96% of use that is beyond gardening.

When gardeners grow their own food at home, we estimate that water use declines by 89% because home grown fruit and vegetables are vastly more efficient in water use compared to those grown on farms. It takes 100,000L of water to produce just 1kg of beef, compared to 48L for a mixture of vegetables.

Highly organic soils hold up to five times as much water as heavily ploughed, heavily fertilised, chemically grown food. So when we grow our own food at home we can cut overall water use by 66%.

In our Heronswood food gardens we have done extensive trials on the amount of water we use and the area needed to become self-sufficient in food. During the hottest summer in the 11th year of the longest drought, we needed to apply 570 litres of water for every square metre of garden. We need supplementary water from December through to April which is about 150 days, so our daily application of water for each square metre of garden is about four litres per square metre each day.

Following our yield trials we found that it only takes 60m² of space to grow the 242kg of fruit and vegetables we consume each year. Our water requirement is 34,200L (ie: 60m² x 570L/m²), which is only 29% of the catchment area of an average house (see table below).

To be sure our experience is relevant to all gardeners in the country, we have provided tables for all capital cities, applying our growing days maps to the applicable summer rainfall. We estimate a 7,000L tank is adequate to provide water storage for 86 days in Sydney and 21 days for Adelaide (see table on following page).

Vegetables and fruit are thirsty (three drip, 850mm+) plants that will not yield or thrive in a (one drip) 500mm rainfall. To grow fruit and vegetables at Heronswood effectively, we use a total of 1,255mm of water per year, or 1,255L/m². This is simple addition of annual rainfall, 655mm and 570mm in supplementary water.

Basic water calculations