Evaporation in Agriculture: How Water Is Lost and How to Stop It

Water is the lifeblood of Australian farming — and evaporation is one of its most persistent enemies. Across every stage of the agricultural water cycle, from storage dams to irrigation channels to the soil surface itself, water is constantly being lost to the atmosphere. Understanding evaporation in agriculture is essential for any farmer or property manager looking to maximise the return on their most valuable resource.

Where Does Agricultural Water Actually Go?

Australian agriculture accounts for approximately 70 percent of the nation’s total water consumption. Yet a significant proportion of that water never reaches the plant root zone. It is lost in transit — through evaporation at multiple points in the supply chain.

There are four main points where evaporation claims agricultural water:

• Open storage dams and reservoirs — the most significant single source of farm evaporation loss
• Open irrigation channels — unlined or exposed channels lose water to both seepage and evaporation
• Overhead irrigation systems — sprinklers operating in hot, windy, or dry conditions can lose 20 to 40 percent of applied water before it reaches the ground
• Bare soil evaporation — after irrigation, water sitting at the surface of hot, bare soil evaporates rapidly before plants can absorb it

Evaporation from On-Farm Water Storage

On-farm storage dams are the foundation of water security for millions of Australian agricultural properties. They collect and hold water for irrigation, stock, domestic use, and fire protection. But open water dams are extremely vulnerable to evaporative loss.

In southern Queensland and northern New South Wales — both major agricultural regions — potential evaporation regularly reaches 1,800 to 2,200 millimetres per year. For a 10-megalitre storage dam with a generous surface area, this can translate to an annual loss of 1.5 to 3 megalitres — water that could irrigate hectares of vegetables, sustain hundreds of head of cattle, or simply be retained as drought reserve.

The financial cost of that loss varies significantly depending on the value and scarcity of water in a given season, but even at modest water market prices, the dollar value of preventable evaporation losses from a single farm dam can run into tens of thousands of dollars annually.

The Problem With Overhead Irrigation

Centre-pivot and lateral-move irrigation systems are widely used across Australian broadacre and horticultural operations. They are efficient in terms of labour and coverage, but they are highly susceptible to evaporation losses when operated under hot, dry, or windy conditions.

Research from agricultural water management agencies indicates that overhead irrigation applied during the middle of the day in 35°C+ temperatures with moderate winds can lose up to 40 percent of applied water to evaporation before reaching the crop canopy or soil surface. This represents not just a water efficiency problem but a direct input cost problem — every lost litre represents irrigators paying to pump water that never benefits the crop.

Strategies to reduce irrigation evaporation include:

• Night-time or early morning irrigation — cooler temperatures and calmer winds dramatically reduce evaporative losses from sprinklers
• Low-trajectory nozzles — reducing droplet travel distance decreases exposure time in the air and reduces drift losses
• Conversion to drip irrigation — subsurface or surface drip systems deliver water directly to the root zone, bypassing surface evaporation almost entirely
• Deficit irrigation scheduling — irrigating to meet actual crop water demand rather than by time or routine reduces total water applied and loss

Soil Evaporation: The Hidden Loss

Even after water successfully reaches the soil, it is not safe from evaporation. In hot conditions, bare or sparsely vegetated soil can lose a significant fraction of applied water through surface evaporation within hours of irrigation.

Mulching is the most effective strategy for reducing soil evaporation. Organic mulch on the soil surface acts as a physical barrier that traps moisture below and dramatically reduces the rate at which the sun and wind can draw it out. Studies have shown that an effective mulch layer can reduce soil evaporation by 50 to 70 percent, increasing the proportion of applied water that reaches plant roots.

Cover crops and minimum-tillage practices also play a role by maintaining soil structure that holds moisture and reducing the bare soil surface area exposed to evaporative stress.

Evapotranspiration: The Combined Challenge

Agronomists and water managers often work with a combined concept called evapotranspiration (ET) — the total water lost from both direct evaporation from soil and water surfaces plus transpiration from plant leaves. ET data, published regularly by the Bureau of Meteorology and state agricultural departments, is the foundation of science-based irrigation scheduling.

By tracking ET for their specific location and crop type, farmers can irrigate precisely to replace what has been lost rather than applying a fixed volume on a calendar schedule. This approach — known as ET-based irrigation scheduling — is one of the most impactful ways to improve overall water use efficiency.

The Case for Covering Your Farm Dam

Of all the evaporation losses in the agricultural water chain, on-farm dam evaporation is often the most cost-effective to address. Unlike redesigning irrigation infrastructure or changing farming practices, a floating dam cover is a single investment that immediately and dramatically cuts losses on an existing asset.

For farms where water storage is the bottleneck — either in volume or in reliability through dry seasons — covering even a portion of the dam surface delivers a measurable return. EvapCo’s team can help you model the return on investment for your specific storage situation, factoring in your local evaporation rate, dam size, and water value.

With over 30 years of dam construction experience through Big Ditch, we understand how farms are built and how water is managed across a wide range of Australian agricultural systems. That knowledge underpins every recommendation we make.

Summary

Evaporation in agriculture occurs at multiple points — from storage dams to irrigation systems to the soil surface. In Australia’s hot, dry climate, these losses add up to a substantial fraction of total water used. Targeted interventions — particularly covering on-farm storage dams, optimising irrigation timing, and improving soil moisture retention — offer the highest return for farmers looking to stretch their water supply further.

Ready to Cut Your Farm’s Evaporation Losses?

EvapCo helps Australian agricultural properties reduce water loss from dams and open water storage. Backed by decades of on-the-ground experience, we offer practical, cost-effective solutions designed for Australian conditions.

Contact EvapCo today to discuss the right evaporation control strategy for your property.

Frequently Asked Questions

How much water is lost to evaporation in Australian agriculture?

Studies suggest that up to 40 to 50 percent of water used in broad-acre irrigation can be lost to evaporation before it reaches the crop root zone, depending on irrigation method, time of day, temperature, and wind speed. Overhead sprinkler systems in hot and windy conditions are the most susceptible to evaporative losses.

What irrigation method loses the least water to evaporation?

Subsurface drip irrigation loses the least water to evaporation because water is delivered directly to the root zone below the soil surface, eliminating surface evaporation almost entirely. Surface drip and micro-irrigation are also more efficient than overhead sprinkler systems.

Does evaporation from irrigation dams affect crop yields?

Yes. When on-farm storage dams lose significant volumes to evaporation, less water is available for irrigation when crops need it most — during summer peak demand. This can directly reduce yields or force farmers to purchase additional water at high market rates during drought periods.