Australia is often described as a dry continent facing inevitable water shortages, yet the reality is far more complex. On a per-person basis, Australia receives vast amounts of rainfall, much of which is lost through evaporation rather than use. This chapter explores the myths surrounding water scarcity, explains why we harvest so little of our rainfall, and shows that the real challenge is not lack of rain but managing evaporation. Understanding how water behaves in our climate is the first step toward practical, local water harvesting solutions.
CHAPTER 4: LOCAL WATER HARVESTING
We are continuously being told that Australia faces severe and growing water shortages. This message has been repeated so often that it is widely accepted as an unquestioned truth. Yet when we step back and look at the actual numbers, a very different picture emerges. On average, the total amount of water available to Australia is far in excess of our basic needs, approaching half a megalitre per person per day. By global standards this is an extraordinary figure.
Very few countries receive anything like this amount of water. Iceland, with its glaciers and high rainfall, tops the list at around 2.8 megalitres per person per day. At the other extreme, countries such as Kuwait receive as little as 30 litres per person per day. Australia sits far closer to the high end of this scale than the low end, yet we continue to frame water as a scarce and failing resource.
THE REAL PUZZLE: WHY DO WE HARVEST SO LITTLE?
If Australia receives so much water, why does it feel as though we are always short of it? The answer lies not in how much rain falls, but in how little of it we actually capture. Of all the rainfall that lands on the continent, we harvest only about one litre in every two thousand. This astonishingly low figure raises an obvious question: why is the proportion so small, and what can we do to improve it?
There are many reasons for this low level of capture. Rain does not fall evenly across the country or at times that conveniently suit our needs. A large proportion of Australia’s rainfall occurs in the northern tropics, where intense seasonal rains quickly run off into rivers and out to sea. Significant rainfall also occurs in the mountainous regions of Tasmania, where the terrain and remoteness make large-scale harvesting difficult or uneconomic.
Our formal water catchments, such as dam systems, cover only a small fraction of the total land area. They are limited by geography, suitable dam sites, and environmental constraints. As a result, vast areas that receive rainfall are effectively ignored by our water harvesting infrastructure.
This is where small-scale, decentralised solutions become important. Rainwater tanks, such as those installed on roof gutters, allow households and buildings to capture water where it falls. These systems do not require large dams or major infrastructure, yet collectively they can make a meaningful contribution to local water security by capturing rainfall that would otherwise be lost.
NOT ALL RAIN IS EQUALLY USEFUL
Another critical misunderstanding is the assumption that all rainfall is equally valuable. In reality, the usefulness of rain depends heavily on how much falls and over what period. The first 10 millimetres or so of rainfall usually does little more than wet the soil surface. In warm and windy conditions, this moisture rapidly evaporates and contributes little to plant growth or water storage.
Rainfall events between roughly 10 and 50 millimetres are often the most beneficial. This amount is usually enough to wet the root zone of plants, where it can be used effectively for growth. However, it typically does not generate significant runoff, meaning it is largely invisible to our dam-based water collection systems.
Heavier rainfall, generally above 50 millimetres, is required before runoff occurs. This is the type of rain that fills rivers and dams and is therefore captured by traditional water infrastructure. Ironically, this means we are harvesting mainly the largest rain events while ignoring the far more frequent smaller rains that are vital for soil moisture and plant health.
EVAPORATION IS NOT ALWAYS LOST WATER
Evaporation is often treated as synonymous with waste, but this is not always the case. In regions with high rainfall and high humidity, evaporated water can return as rainfall nearby. The Amazon rainforest provides a striking example. In this system, an estimated 60 to 70 percent of rainfall is recycled water that has previously evaporated from vegetation and soil.
In these environments, evaporation is part of a stable and productive water cycle. Water evaporates, forms clouds, and falls again as rain, supporting dense vegetation and rich ecosystems. In such cases, evaporation is not truly lost; it is merely redistributed within the system.
In contrast, in dry or arid regions, or after long dry periods, evaporated water is far more likely to be carried away by wind and dispersed over vast distances. In these conditions, evaporation represents a genuine loss from the local system, contributing little or nothing to future rainfall.
THE REAL ISSUE: EXCESSIVE EVAPORATION
Australia’s fundamental water problem is not a lack of rainfall, but excessive evaporation. In much of the country, evaporation exceeds rainfall for most of the year. You do not have to travel far inland before evaporation is double the annual rainfall. Closer to the centre of the continent, evaporation can be ten times greater than rainfall.
This imbalance makes it extremely difficult to store and use water effectively using conventional methods. Large, open dams lose enormous volumes of water to evaporation, particularly during hot and dry periods. As a result, much of the rain that does fall cannot be readily captured or retained for later use.
The critical question, then, is whether we simply accept this excessive evaporation as an unavoidable fact of life, or whether we can do something about it.
VEGETATION HOLDS THE CLUE
If we look closely at areas with extreme evaporation, where losses far exceed rainfall, an important observation emerges. These regions are not empty wastelands. In many cases, they support extensive and resilient vegetation. This immediately tells us that water is being captured, stored, and used in ways that are not reflected in our conventional water accounting.
At first glance, it is tempting to attribute this vegetation solely to specialised plant adaptations. Many plants have evolved mechanisms to reduce water loss, such as waxy leaves, deep root systems, or seasonal dormancy. While these adaptations are important, they would be ineffective without a deeper, underlying process.
The key mechanism lies in how water is stored in soil and cycled through living systems. Vegetation shades the soil, reducing surface temperatures and evaporation. Organic matter improves soil structure, increasing its ability to hold moisture. Roots and soil organisms create pathways that allow water to infiltrate and remain available for longer periods.
These natural systems show us that water does not need to be stored only in large, open reservoirs. It can be stored in soils, landscapes, and biological systems, where evaporation losses are far lower and water remains available to plants over extended periods.
TOWARD A DIFFERENT WAY OF THINKING
The lesson from local water harvesting is clear. Australia does not suffer from a simple shortage of rain. Instead, we suffer from a mismatch between our climate and the water management technologies we rely on. Systems developed in cooler, wetter, and more mountainous regions of the world are poorly suited to a flat continent exposed to long periods of intense heat.
By focusing almost exclusively on large dams and centralised infrastructure, we have ignored the vast potential of local rainfall, soil moisture storage, and distributed harvesting systems. Small rains, which make up the bulk of our rainfall events, pass through the landscape largely unused.
A more resilient approach to water management must work with natural processes rather than against them. It must aim to slow water down, store it in the landscape, reduce evaporation, and make use of rainfall wherever it falls. Local water harvesting is not a single technology but a shift in thinking, one that recognises water as part of a living system rather than a commodity to be captured only at the largest scale.
Understanding these principles is the foundation of the Waterright philosophy. Only by addressing evaporation, soil moisture, and local storage can Australia hope to make effective use of the water it already receives.
