Water is money. In rural Australia, this is not a metaphor — it is a practical reality that plays out every single day. Yet one of the largest ongoing costs many farmers face is invisible, silent, and almost completely preventable: the financial loss from dam evaporation. Most property owners have never calculated exactly how much water their dams lose each year, or what that loss is actually worth. The numbers, once you look at them, are often startling.

The Invisible Cost You’ve Been Ignoring

Unlike a broken fence, a failed pump, or a diseased crop, evaporation does not announce itself. It simply takes water, slowly and relentlessly, every day of every year, and particularly hard during the hot months when you need your storage most. Because the loss is gradual and silent, it rarely prompts an immediate financial response — but the cumulative cost is real, significant, and compounding year on year.

Let’s be specific about what that cost looks like in practical terms.

Calculating the Cost: A Worked Example

Take a mid-sized property in inland New South Wales. The farm has a 10-megalitre dam used for stock water and supplemental irrigation. The local area receives average annual potential evaporation of approximately 1,800 mm per year. The dam surface area is roughly 2,000 square metres.

The calculation is straightforward:

Annual potential evaporation: 1,800 mm = 1.8 metres
Dam surface area: 2,000 m²
Estimated annual evaporation loss: 1.8 m × 2,000 m² = 3,600 m³ = 3.6 megalitres per year

For context, 3.6 megalitres is more than a third of that dam’s total storage capacity — lost to the sky every single year, without drought, without a leak, and without any equipment failure.

What Is That Water Actually Worth?

Placing a dollar value on lost water is complicated because water values vary so much by use, region, and season. However, there are several ways to frame the financial impact:

Irrigation water value

In the southern Murray-Darling Basin, temporary water allocation prices have ranged from under $100 per megalitre in years of good inflows to over $1,000 per megalitre during the 2018-2019 drought. At $300/ML — a moderate benchmark — 3.6 megalitres of annual evaporation loss represents a $1,080 annual cost, every year, on that single dam.

Trucked water replacement cost

For properties that lose critical stock water to evaporation during drought, the alternative is often buying and trucking water. At typical rural water cartage costs of $150 to $300 per 10,000 litres, replacing 3.6 megalitres by truck would cost between $54,000 and $108,000. That is the true cost of running out of stored water — and it makes the investment in evaporation prevention look extraordinarily valuable.

Livestock production value

Water stress affects animal welfare, weight gain, milk production, and reproductive rates. When dams run short in late summer — exactly when evaporation is at its peak — the downstream financial effects on herd productivity can far exceed the direct cost of the water itself.

The Compounding Cost Over Time

Evaporation costs do not sit still. As climate change drives higher temperatures and more intense drought conditions, annual evaporation rates in many parts of Australia are increasing. What cost $1,080 per year today may cost $1,500 per year in a decade — before you factor in rising water market values as scarcity increases.

Over a 20-year property planning horizon, cumulative evaporation losses from a single unprotected mid-sized farm dam can easily run to 50 to 100 megalitres of water — a volume that would fill the same dam five to ten times over.

The Return on Investment for Evaporation Control

When framed this way, the investment case for evaporation control becomes clear. A floating dam cover installed on a 2,000 m² dam surface — one of the most effective evaporation solutions available — can reduce evaporation losses by 70 to 90 percent. Over a product lifespan of 15 to 25 years, the water saved, multiplied by even a conservative water value, typically delivers a strong return on the initial investment.

Simpler measures — strategic windbreaks, partial shade structures, and evaporation suppressant products — provide lower initial cost options that still deliver meaningful annual water savings.

Additional Hidden Costs of Dam Evaporation

Beyond the direct water value calculation, evaporation losses carry other financial consequences that are rarely counted:

Reduced property value — dams that are known to run dry in summer reduce the assessed value of rural properties and their attractiveness to buyers
Increased pumping costs — as water levels fall, pumps draw from lower depths and work harder, increasing energy costs and wear
Water quality degradation — concentrated water from evaporation losses results in higher salinity and nutrient levels, which can affect water suitability for stock and irrigation
Emergency response costs — sourcing emergency water during drought is expensive, stressful, and often involves infrastructure costs like temporary pipelines or additional storage

Making the Decision to Act

The first step is knowing your own numbers. Use local Bureau of Meteorology evaporation data to estimate your dam’s annual loss. Multiply by the surface area, convert to megalitres, and assign a conservative value to each megalitre. The result is a clear annual cost figure that makes the decision to invest in evaporation control straightforward.

The team at EvapCo can help you run this calculation for your specific situation and identify the most cost-effective solution — whether that is a full floating cover, a partial solution, or a product combination suited to your dam size and use case.

Summary

Dam evaporation is a significant, ongoing, and often underestimated financial cost for Australian farmers. A single mid-sized farm dam can lose several megalitres of water per year to evaporation — water worth hundreds to thousands of dollars at current market values, and potentially tens of thousands if replacement by trucking is required. Evaporation control delivers a clear return on investment and protects farm productivity and property values over the long term.

Find Out What Evaporation Is Costing You

EvapCo offers free consultations to help Australian property owners understand their evaporation losses and identify the right solutions. Don’t wait until your dam runs dry.

Talk to the EvapCo team today.

Frequently Asked Questions

How much does dam evaporation cost Australian farmers each year?

The cost depends on dam size, location, and the value of water. A 10-megalitre farm dam in inland NSW or Queensland can lose 1.5 to 3 megalitres per year to evaporation. At temporary water market prices of $100 to $500 per megalitre, that represents $150 to $1,500 in lost water annually — and significantly more during drought when prices spike.

Is investing in evaporation control worth it for small farm dams?

For small dams used primarily for stock water, the payback period for a full floating cover may be longer. However, partial covers, shade structures, and evaporation suppressant products offer lower-cost alternatives that still deliver meaningful water savings. For dams used for irrigation, the return on investment is typically strong.

What is the value of one megalitre of water in Australia?

Water values vary enormously by region and water entitlement type. Temporary water trade prices in the Murray-Darling Basin have ranged from under $50 per megalitre in wet years to over $1,000 per megalitre during severe drought. For property owners relying on self-supply from dams, the cost of replacement (trucking water or emergency bore drilling) can be far higher.