While companies use water balances to manage their current water usage, a water balance can also be developed to forecast future water needs – which in turn guide infrastructure planning and design.

Simon Bruton, senior hydrologist at SRK Consulting South Africa (SA), highlighted that water balances are an important tool for measuring the potential impacts and risks associated with extreme climate events and climate change forecasts.

“You can’t manage what you don’t measure, so water balances are really the ‘balance books’ of effective water management,” said Bruton.

“They are critical for understanding and reporting water sources, uses and losses across an operation, including monitoring gaps – particularly with growing pressure on available freshwater resources coupled with increasing impacts from land use change, pollution and climate change.”

Supply and quality

Many industries focus on the security of water supply, while others – whose impact on water quality is greater – need to also consider their discharge of stored water and the risk of spills.

“Mining, for instance, has to manage its water footprint and minimise its impact by separating clean from dirty stormwater, along with any impacted or discharge waters,” he said.

The nature of the water balances developed by a hydrologist can vary widely, he noted, based on the needs and affordability of the client.

“At the one end, a small water balance can cover piped water reticulation within the confines of a small factory,” he explained. “At the other end of the scale are site-wide water balances for a mine; these cover piped reticulation, rainfall, evaporation, runoff, groundwater and water storage across expansive sites.”

Opportunity to improve

Importantly, the water balance may highlight opportunities for the increased recycling of water, saving on costs of new water, and reducing volumes of wastewater which are costly to manage, store and treat. Bruton explained that, once a water balance model of current water reticulation and use is operational and calibrated, the modeller can then generate a forecasting model to investigate future scenarios covering impacts on water use, water pollution, storage needs and risk of spill from storage.

“Water balances may also need to account for transfer rate, whether in pipes, along stormwater channels, over spillways or out of penstocks,” he said.

“The question to be answered is this: Can the current or planned infrastructure handle the water transfer rates and storage volumes that will be required if production is increased, if new infrastructure is added, or if the site is subjected to extreme rainfall events with climate forecasts applied?”

Simulating solutions

Changes in infrastructure, production and extreme events such as droughts, extreme rainfall and floods can then be applied to the model to investigate impacts and test innovative solutions.

“Stochastic modelling can also be applied which introduces synthetic variability based on the statistics of the input records to the model,” he said. “This allows multiple realisations of the simulation to be run.”

The outputs are then plotted as probabilities which can be used to evaluate risk, he noted. This risk – which is essentially the level of certainty related to water storage for supply or unplanned discharge – can then be evaluated against cost to inform management decisions on expenditure versus risk.