The water mix invites us to diversify water sources, but also to question the uses they support. Behind the promise of additional supplies lie different ways of approaching water management.
In its 2025 Activity Report, the International Office for Water (OiEau) highlights the water mix, drawing an analogy with the energy mix. The approach combines surface water, groundwater, soil moisture and non-conventional resources, alongside supply diversification and demand management. But does it help adapt water use to basin limits, or push those limits to maintain existing uses?
The water mix is not an entirely new idea. As early as the 2000s, South Africa considered non-conventional resources to anticipate its future needs. Other territories, including Indonesia and California, have sought to diversify supplies and reduce their dependence on surface water. Singapore combines local catchments, imports, reclaimed water and desalination, while also managing demand.
Integrating the concept into Integrated Water Resources Management (IWRM) therefore raises a question: what does it add to an already integrated approach? The answer depends on how we define scarcity. If scarcity simply means insufficient supply, the water mix risks becoming a programme for additional production. If it reflects an imbalance between resources, uses and ecosystems, the concept could encourage a deeper reassessment of their relationships.
The issue therefore extends beyond technical diversification. It concerns whether new sources help adapt water use to basin limits, or simply allow existing uses to continue.
Diversifying sources does not mean that available volumes add up without consequences. Treated wastewater, for example, may already feed a river. Reusing it changes its destination rather than necessarily creating an additional resource. This matters particularly during dry periods, when effluent helps sustain river flows.
Assessments must therefore consider avoided withdrawals, the previous destination of discharges and actual consumption. Additional supply can also encourage new uses. Researcher Marielle Montginoul has observed this rebound effect in wastewater reuse schemes. Desalination presents another set of trade-offs: it diversifies supplies, but requires energy, investment and arrangements for managing brine discharges.
These constraints do not invalidate the solutions. They show how diversification redistributes dependencies. Assessing the water mix therefore requires distinguishing local supply security from benefits across the wider basin. Producing more water is not enough; the assessment must identify which pressures disappear and which shift elsewhere.
Making these choices requires a sound understanding of water resources. OiEau’s report emphasises reliable, interoperable data to support decisions. Bringing together river flows, groundwater levels, water quality, withdrawals and discharges helps assess the effects of reuse. Distinguishing installed capacity from actual production also helps verify expected substitutions. Each territory should therefore use the water mix as a decision-making framework, rather than an automatic answer.
However, integrating the mix into IWRM does not automatically make decisions collective. Planning must precede projects, rather than simply justify them. Consultation should not merely secure acceptance of a predetermined solution. It should open discussion about priorities, alternatives and allocation rules.
The distinction matters: the mix describes how available resources fit together, while integrated management must organise the trade-offs between users and ecosystems.
