Water Stewardship in Modern Mining: Achieving Net-Positive in Arid Regions

Mining and water have always had a tense relationship. The industry consumes enormous volumes — for mineral processing, dust suppression, slurry transport, and camp operations — while often operating in precisely the regions where water is scarcest. Sterling Ore's African operations faced this paradox acutely: our Mopani Ridge copper facility and Witwatersrand gold operations sit in semi-arid catchments where annual rainfall averages less than 500mm and competition for water rights from agricultural communities is intensifying. Two years ago, we committed to achieving net-positive water impact by 2028. We reached the milestone in early 2026 — two years ahead of schedule.

What "Net-Positive" Actually Means

The term gets thrown around loosely in sustainability reports, so let's define it precisely. A mining operation is net water-positive when the volume of water it returns to the catchment in usable form — through treatment, recharge, or alternative supply development — exceeds the volume it withdraws for operational use, after accounting for evaporative and incorporative losses.

This is harder than it sounds. Mining operations don't just use water; they change its chemistry. Process water picks up dissolved metals, sulphates, and suspended solids. Tailings storage facilities lose water to evaporation and entrainment. Pit dewatering can lower local water tables, reducing the baseflow available to downstream users. Achieving net-positive means solving all of these problems simultaneously — and measuring the results with enough rigour that an external auditor can verify the claims.

At Sterling Ore, our net-positive accounting follows the Water Accounting Framework developed by the Minerals Council, with third-party verification by an independent hydrogeology consultancy. Every megalitre is tracked from source to discharge, and our annual water balance is published as part of our sustainability disclosures.

The Technology Stack: Three Pillars

Our water-positive outcome rests on three interlocking technology investments, each addressing a different part of the water cycle.

1. Closed-Loop Process Water Treatment

The single largest lever was converting Mopani Ridge from a once-through process water system to a closed-loop configuration. In the old arrangement, process water made a single pass through the flotation circuit and was then discharged to a lined evaporation pond — losing approximately 1.2 megalitres per day to evaporation during the dry season, with the residual brine requiring hazardous-waste management.

The new system, commissioned in Q3 2024, incorporates high-recovery reverse osmosis (HRRO) with a proprietary anti-scalant formulation developed specifically for the sulphate-rich chemistry of copper flotation tailings. HRRO achieves 92–95% recovery — conventional RO typically manages 75–85% — by operating at higher pressures and using staged membrane arrays that treat the concentrate stream from the first stage rather than discharging it. The permeate is polished through activated carbon and returned to the process circuit; the residual concentrate, now reduced to roughly 5–8% of the original volume, goes to a crystalliser that produces a dry salt cake suitable for controlled landfill disposal.

The result: Mopani Ridge reduced its raw water intake by 76%, from 1.2 ML/day to approximately 0.29 ML/day, while maintaining identical production throughput. The capital cost of the HRRO plant — $4.8 million — was recovered within 14 months through reduced water procurement costs and eliminated brine disposal fees.

2. Managed Aquifer Recharge at Witwatersrand

Our Witwatersrand gold operation presented a different challenge. Unlike Mopani's continuous process-water demand, the primary water issue at Witwatersrand was seasonal stormwater management. During the November–March wet season, the site receives roughly 85% of its annual rainfall in intense convective storms. Historically, this stormwater was captured in settlement ponds, treated for sediment, and discharged to the local watercourse — compliant with the site's water-use licence, but a missed opportunity.

In partnership with the regional water authority and a hydrogeology team from the University of Pretoria, we designed and constructed a managed aquifer recharge (MAR) scheme that diverts treated stormwater into a shallow aquifer underlying the site. The aquifer — a weathered dolomite formation with high transmissivity and approximately 2.5 million cubic metres of available storage — acts as a natural reservoir, buffering wet-season inflows against dry-season abstraction by downstream agricultural users.

The MAR scheme injected 187 megalitres into the aquifer during the 2024–25 wet season — water that would otherwise have been lost as surface runoff to the Indian Ocean. During the subsequent dry season, the regional water authority licenced abstraction of 142 megalitres for irrigation, representing a net addition to the catchment's utilisable water budget. The remaining 45 megalitres stayed in the aquifer as stored volume, raising local groundwater levels by an average of 1.2 metres and improving baseflow to a perennial spring that serves three downstream villages.

3. Community Borehole Programme

The third pillar is the least technologically sophisticated but, in many ways, the most impactful. In partnership with the district water authority, we funded and drilled 12 community boreholes serving approximately 8,400 people in villages within a 15-kilometre radius of our operations. Each borehole is equipped with a solar-powered pump, a 10,000-litre elevated storage tank, and a tap stand with potable-quality water treated through a small-scale ultrafiltration unit.

The boreholes produce a combined average of 94 megalitres per year of potable water that did not previously exist in these communities — water that was always present in the aquifer but inaccessible without the capital investment to drill and equip the boreholes. Sterling Ore funds ongoing maintenance through a community water committee, with technical support provided by our environmental team, but the infrastructure is owned and operated by the villages themselves.

Under the Water Accounting Framework, this community supply volume is credited against our operational withdrawals because it represents water that our capital expenditure made available to the catchment that would not otherwise be accessible. It is the single largest contributor to our net-positive balance, accounting for roughly 40% of the surplus.

The Monitoring Infrastructure

None of this would be credible without measurement infrastructure that can survive external audit. We operate a network of 34 continuous-monitoring stations across Mopani Ridge and Witwatersrand, measuring flow rates, water levels, and a standard suite of water-quality parameters (pH, conductivity, dissolved oxygen, turbidity, temperature) at 15-minute intervals. Data is transmitted via LoRaWAN to a central SCADA system and mirrored to a cloud dashboard accessible to the regional water authority.

The monitoring network cost approximately $620,000 to deploy and has an annual operating cost of roughly $45,000 — a fraction of the savings generated by the closed-loop treatment system alone. Its value, however, extends beyond operational efficiency. The data stream provides an independently verifiable record of our water balance that underpins the credibility of our net-positive claim with regulators, investors, and local communities.

One unexpected benefit: the monitoring network detected a rising salinity trend in the Witwatersrand aquifer in Q2 2025 that turned out to originate from an upstream agricultural operation's fertiliser management practices, not from our activities. We were able to share the data with the water authority and the farming cooperative, leading to a collaborative adjustment in fertiliser application that improved both water quality and farm input costs. This kind of data-driven catchment stewardship would not have been possible without the monitoring investment.

Community Partnerships: The Non-Negotiable Element

Technology can solve the engineering side of water stewardship. It cannot solve the social side. Our operations sit within catchments where water is not just an environmental input — it is the foundation of subsistence agriculture, livestock watering, and domestic life for communities that have lived here for generations. A net-positive water balance that benefits only the mining company is, in practice, a licence-to-operate risk, not an achievement.

Our approach has been to treat community water security as a co-equal objective, not a CSR afterthought. This manifests in three concrete commitments:

• Community water committee representation: Each village within our catchment area elects two representatives to a water stewardship committee that meets quarterly with our environmental manager and the regional water authority. The committee reviews monitoring data, discusses emerging issues, and has a formal consultative role in any proposed changes to our water management plan.
• Transparent, real-time data access: Water quality and quantity data from our monitoring network is publicly accessible through a simplified dashboard interface (available in English, Swahili, and Afrikaans). If a community member asks whether the mine is affecting their water, they can check the data themselves — they don't need to take our word for it.
• Grievance mechanism with teeth: Any community member can file a water-related complaint through a toll-free SMS hotline. Every complaint triggers a formal investigation within 72 hours, with findings reported back to the complainant and the water committee. Since the mechanism launched in 2023, 17 complaints have been filed; 14 were resolved within the 72-hour window, and three escalated to mediation with the district water authority, all of which were settled without litigation.

What Didn't Work

Sustainability narratives are prone to sanitisation; we think it is more useful to be honest about what failed. Two initiatives did not deliver as planned:

Atmospheric water generators (AWGs): In 2023, we piloted two AWG units — machines that extract water from humid air using condensation — at our Mopani Ridge camp, with the intention of offsetting potable water demand. The concept is elegant: free water from the air, no catchment impact. The reality in a semi-arid climate was less impressive. Average relative humidity during the dry season (May–October) was too low for efficient operation, and the units produced approximately 15% of their rated output. At a capital cost of $85,000 per unit, the cost per litre of water produced was roughly 12x the cost of the HRRO-treated water that replaced it. The units have been decommissioned and donated to a coastal research station in Mombasa, where humidity is consistently above 70% and they perform closer to specification.

Constructed wetlands for tailings seepage: We designed a pilot-scale constructed wetland to treat low-volume seepage from the Witwatersrand tailings facility — the idea being that aquatic plants and microbial communities in the wetland substrate would naturally attenuate dissolved metals before the water reached the local watercourse. While the system did remove approximately 60% of dissolved iron and manganese, it proved ineffective against sulphate (removal below 10%) and required significantly more maintenance than anticipated. After 18 months, we concluded that the wetland was a well-intentioned but underperforming intervention and redirected the budget toward expanding the MAR scheme, which delivered far more water-quantity benefit per dollar spent.

The Economics of Net-Positive

One of the persistent myths in mining is that environmental leadership costs money that could otherwise flow to shareholders. Our experience argues the opposite. The table below summarises the financial outcomes of our water stewardship investments:

• HRRO closed-loop system: $4.8M capital, $1.7M/year operational savings (water procurement and brine disposal), 14-month payback, cumulative net savings of ~$2.1M through Q1 2026.
• Managed aquifer recharge scheme: $2.3M capital, co-funded 40% by the regional water authority. Ongoing operational cost approximately $60K/year. Avoided cost of alternative water-supply infrastructure: estimated $4.5–6M (the water authority's cost to develop equivalent storage capacity through conventional dam construction).
• Community borehole programme: $480K capital (12 boreholes), $35K/year operating contribution. Intangible return: strengthened community relations, zero water-related work stoppages or protests since programme inception, and a demonstrable contribution to social licence that has materially de-risked our mining-permit renewal processes.
• Monitoring network: $620K capital, $45K/year operating. Value: independently verified data supporting regulatory compliance, investor confidence, and the credibility of our sustainability disclosures — plus the early detection of the upstream salinity issue that prevented a potential community-relations crisis.

In aggregate, our water stewardship programme has generated a positive net present value even before accounting for the harder-to-quantify benefits of regulatory goodwill, community trust, and investor confidence. Water stewardship, done properly, is not a cost centre — it's a competitive advantage.

The Bottom Line

Achieving net-positive water impact in a semi-arid mining region is difficult but achievable. It requires meaningful capital investment, rigorous monitoring, genuine community partnership, and a willingness to admit when a promising technology doesn't deliver in real-world conditions. The payoff — in operational efficiency, regulatory confidence, community trust, and genuine environmental benefit — more than justifies the effort.

Sterling Ore reached net-positive two years ahead of schedule. The real test now is maintaining it — and sharing what we've learned so that other operators in water-stressed regions can follow the same path, hopefully faster and with fewer false starts.