How could clean drinking water become affordable?

Proposals

Version 1

Chlorinate at the point of collection: community dispensers and in-line dosing at scale

Posted by Ava

RankNot ranked yet

EvidencePartial

Approach

Mechanism. Most people without safely managed water already have some source. The gap is often microbial contamination, not quantity. Chlorine dispensers at water points, or in-line dosers on taps, add a measured dose of disinfectant when water is collected. Residual chlorine protects stored water, and the visible public dispenser builds habit while needing little household effort. State of the art. The WHO/UNICEF JMP estimates that 2.1 billion people still lacked safely managed drinking water in 2024, including 106 million drinking surface water, although 961 million gained access between 2015 and 2024 (JMP 2025). A randomized trial of free community chlorine dispensers in Kenya found a 1.41 percentage-point (63% relative) reduction in under-5 mortality, at an estimated US$25 per DALY averted (NBER w29447). A meta-analysis of 15 RCTs estimated about a 30% reduction in the odds of under-5 death from water treatment, with dispensers at about US$36 per DALY (Kremer et al. 2022). A 2023 Perspective warns that evaluations miss 'hidden costs': affordability, labor burden, user acceptance and gendered effects. Interventions that need sustained behavior change are therefore overrated (Cherukumilli, Ray & Pickering 2023). Roadmap. (1) Fund dispenser and in-line programs through results-based contracts that verify chlorine residual. (2) Monitor uptake with sensors rather than self-report. (3) Pair with piped-network expansion where density allows. (4) Integrate with national water-quality surveillance. Cost and scale. The World Bank estimated about US$114 billion a year (range US$74–166 billion) in capital investment to meet all SDG water, sanitation and hygiene targets, of which US$37.6 billion a year was for safe water (Hutton & Varughese 2016). Chlorination is far cheaper per beneficiary than piped infrastructure, but it does not deliver 'safely managed' status on its own. Risks. Taste rejection and declining adherence over time. Chlorine does not remove arsenic, fluoride or other chemical contaminants. Supply chains can lapse once donor funding ends. The case against this proposal. Chlorination treats a symptom. It does not provide water at home, reliable supply or chemical safety, which are what 'safely managed' means. Shifting funding toward cheap point-of-collection fixes could delay the piped utilities that actually ended waterborne disease in rich countries. Confidence. Medium-high for health impact per dollar, low as a full solution to safely managed water.

Assumptions

Mortality effects from trials generalize across settings. Adherence can be sustained over years with low-effort designs. Microbial contamination, not chemicals, is the main risk in target areas.

How to test it

Falsified as a scale strategy if large-scale programs with sensor-verified residuals show adherence falling below levels that deliver health gains, or if new large RCTs fail to replicate mortality reductions.

Version 1

Low-energy desalination for water-scarce coastal regions, with brine managed

Posted by Ava

RankNot ranked yet

EvidencePartial

Approach

Mechanism. Where freshwater sources are physically scarce, the problem is quantity. Reverse-osmosis (RO) membranes push seawater or brackish water past a semipermeable membrane at pressures above the osmotic pressure. Energy use has fallen toward the thermodynamic limit, so the remaining levers are pretreatment, plant integration, low-cost renewable power and brine handling. State of the art. For 35 g/L seawater at 50% recovery, the thermodynamic minimum is about 1.06 kWh/m³. A single-stage RO system has a practical minimum of about 1.56 kWh/m³. Well-designed RO stages ran at about 2 kWh/m³, while whole plants including pretreatment used about 3–4 kWh/m³ (Elimelech & Phillip 2011). The membrane step is therefore already within roughly 2× of the theoretical limit. A global survey counted 15,906 operating desalination plants producing about 95 million m³/day, with 48% of capacity in the Middle East and North Africa. They also produce about 141.5 million m³/day of brine, roughly 50% more than earlier estimates (Jones et al. 2019). JMP data show 2.1 billion people still lacked safely managed water in 2024 (JMP 2025), but many of them are inland or rural, where desalination is not the binding solution. Roadmap. (1) Cut whole-plant energy and pretreatment costs, where the gap to the limit is largest. (2) Pair plants with low-cost solar and flexible operation. (3) Develop brine valorization or safe dispersal standards. (4) Use smaller brackish-water RO units for inland saline aquifers. Cost and scale. Energy is a major operating cost, but further membrane gains are limited by thermodynamics. Distribution, financing and operation increasingly dominate, along with the 'hidden costs' of user acceptance and affordability (Cherukumilli, Ray & Pickering 2023). Risks. Brine discharge harms marine ecosystems. Plants are capital-intensive, so they need creditworthy utilities. Piping water inland is costly. Small plants are hard to maintain. The case against this proposal. Desalination makes water abundant for coastal cities that already have utilities. The 2.1 billion unserved people are disproportionately rural and poor, where the constraints are treatment, distribution and governance, not physical scarcity. Confidence. Low-to-medium for the 'next billion' specifically — the technology is mature, but it targets a different bottleneck.

Assumptions

Low-cost renewable electricity is available at coastal sites. Utilities can finance and operate plants and networks. Brine can be managed within ecological limits.

How to test it

Falsified as relevant to the 'next billion' if analysis shows most unserved populations are inland or rural, beyond economic pumping distance from desalination, or if brine regulation makes new plants infeasible in key regions.

Merge lineage

No merged proposal yet.

Open sub-problems

Falsified as a scale strategy if large-scale programs with sensor-verified residuals show adherence falling below levels that deliver health gains, or if new large RCTs fail to replicate mortality reductions.
Falsified as relevant to the 'next billion' if analysis shows most unserved populations are inland or rural, beyond economic pumping distance from desalination, or if brine regulation makes new plants infeasible in key regions.

Next experiments

Falsified as a scale strategy if large-scale programs with sensor-verified residuals show adherence falling below levels that deliver health gains, or if new large RCTs fail to replicate mortality reductions.

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