Evaporation in Mining and Industrial Water Storage in Australia

Water is a critical input for Australian mining and industry, and in the hot, dry regions where most mines sit, evaporation from mining and industrial water storage is a constant drain. It is an operating cost, a compliance issue and, increasingly, a sustainability reporting item.

Why are mine sites so exposed to evaporation?

Mining operations usually run several types of open water storage on or near site:

• Process water dams: water for ore processing, mineral separation and dust suppression.
• Tailings storage facilities (TSFs): the water-saturated waste slurry left after processing.
• Clean water dams: potable and utility water for the workforce and site infrastructure.
• Stormwater basins: runoff from disturbed areas held before treatment or reuse.

All of these are open to the atmosphere. They face the same forces as farm dams, but at a larger scale and with bigger consequences when water runs short or quality limits are missed.

Average annual pan evaporation exceeds 2,500 mm across much of the Pilbara, the Goldfields, outback South Australia and inland Queensland, as shown on the Bureau of Meteorology evaporation maps.

A tailings dam with a 50 hectare surface under 2,500 mm of pan evaporation and a typical 0.7 pan coefficient loses roughly 875 megalitres a year. That volume returns every year the storage stays open.

The financial impact at scale

On a farm dam, evaporation is measured in megalitres. On a large mine, the same process plays out across hundreds of hectares of open water.

Licensed allocations from groundwater or surface water are fixed and costly. Water lost from open storage must be replaced from entitlements, from trucked supply at remote sites, or by cutting other operational uses. Expressed in megalitres and multiplied by the full cost of supply, evaporation becomes a material line in site operating costs.

How does evaporation affect tailings water chemistry?

Tailings water often carries dissolved metals, process chemicals and acid mine drainage products. As evaporation reduces the volume, those contaminants become more concentrated and can approach limits set in environmental licences.

Higher concentrations can trigger extra treatment, compliance risk and, in extreme cases, slowdowns while water chemistry is brought back into range. Reducing evaporation from tailings storage is therefore a risk management tool, not only a water saving.

Regulatory drivers: water balance and licence conditions

Mining operations work under water balance and licence conditions set by state regulators such as the WA Environmental Protection Authority and the NSW EPA. Sites must show that water use, release and storage stay within agreed limits.

Evaporation is a key term in every site water balance. Where it is high and uncontrolled, predictions become less reliable, the risk of shortfall in dry periods rises and annual reporting carries more uncertainty. Controlling it makes the balance easier to manage and defend.

Evaporation control options at industrial scale

How effective are floating geomembrane covers?

High-density polyethylene (HDPE) is a tough, UV-stabilised plastic used for liners and floating covers. Continuous floating covers cut evaporation by 70 to over 90% and can be made to fit irregular storages. They also keep rain out of covered storages, which reduces the volume needing treatment.

Where do shade balls suit mine and industrial storages?

Shade balls are floating plastic spheres that cover a water surface to block sunlight and wind. They suit clean water and process storages where a fixed cover would get in the way of pumps or level changes. The Los Angeles Department of Water and Power used 96 million shade balls on the LA Reservoir. Our shade balls vs floating covers comparison sets out where each fits.

When is evaporation deliberately used on a mine?

Some processes use evaporation ponds on purpose to reduce liquid waste volume. There the goal is controlled evaporation, keeping the rate and pond conditions within environmental limits rather than suppressing loss.

Can storage design reduce evaporation?

Yes. Where a storage is still being designed, maximising depth relative to surface area cuts evaporation per megalitre stored for the life of the facility. Lindsey Hughson and the Big Ditch team have worked on mine water storage problems, including the 100 megalitre processing dam liner solution in our Roy Hill mining case study.

Sustainability reporting and ESG

Water stewardship is now a core part of ESG (environmental, social and governance) reporting for Australian miners. Investors and customers increasingly expect operations to show they manage avoidable losses, and evaporation is one of the most visible.

An evaporation control program gives measurable water savings to report, alongside lower operating cost and compliance risk.

Frequently Asked Questions

How does evaporation affect water management on Australian mine sites?

Mines in arid and semi-arid regions can lose hundreds of megalitres a year from large open storages. That water must be replaced at a cost, and evaporation also concentrates contaminants in tailings water, which adds water quality and compliance risk.

What are the best evaporation controls for large mining dams?

HDPE floating covers give the largest saving on storages they can fit. Shade balls suit storages with changing levels or equipment in the water. Deeper storage design helps at the planning stage. The right choice depends on the dam’s purpose, chemistry and access needs.

Does reducing evaporation help with environmental compliance?

Yes. Less evaporation means lower contaminant concentration in stored water, a more predictable water balance and less risk of shortfall in dry periods, all of which make licence conditions easier to meet.

Losing site water to evaporation from process or tailings storages? Book a site inspection with Big Ditch to scope covers or storage redesign for your operation.