Technical considerations for saving lives
Clean water is an engineering problem and a community problem at the same time. Our technical team dives into the science; each local partner knows what their community will actually use. We iterate between the two — often five times over — until a solution is scientifically sound, genuinely wanted, and built to last. This is where we show that work.
We don’t just apply academic science and engineering — we add systems thinking and economics, and we design hand-in-hand with local NGOs so every solution is practical. That means iterating with the community, and usually starting with a pilot, until it works in the real world.
However deep you want to go, there’s a path
See what we do and where — the map, the projects, and the people behind them.
Explore our work →See what each solution really costs per person per year — and judge the impact-per-dollar yourself.
See the economics →Compare every solution by problem, dive into the technical briefs, or request one directly.
Compare solutions →What does clean water actually cost?
We obsess over impact-per-dollar. Here’s the approximate cost to give one person safe water for a year — the initial investment spread over each system’s lifetime, plus upkeep. Judge for yourself.
| Solution | Location | Initial investment | People reached | Unique benefit | $ / person / yr |
|---|---|---|---|---|---|
| Ultrafiltration + UV village system | Philippines | $533 | ~200 | Two layers of protection; easy to maintain | ~$0.67 |
| School ultrafiltration system | Cambodia | ~$700 | 200+ | Simple; the lowest cost per person | ~$0.55 |
| HDPE distribution + pathogen removal | Papua New Guinea | ~$25,000 | ~5,000 | Reaches a whole rural community | ~$0.60 |
| Electricity-free custom filtration system | DR Congo (Goma) | ~$200 | ~20 | Highest overall impact; fully portable | ~$2.50 |
| Household biosand filter | Cambodia | ~$100 | ~5 | Simple and durable; no upkeep cost | ~$2.00 |
$ per person per year spreads each system’s initial investment across its expected lifetime and adds annual maintenance and power — a fairer comparison than upfront cost alone. Assumptions: Philippines UF+UV — ~5-yr life, ~$30/yr, ~200 daily users; Cambodia school UF — ~10-yr life, ~$40/yr; PNG distribution — ~10-yr life, ~$500/yr, design still in progress; DR Congo (Goma) — a custom system (a Sawyer membrane filter, buckets, a shared 150–200 L storage drum, and a Q-Drum transporter) shared by 4–5 families, ~4-yr life (3–5 typical), no maintenance cost; Cambodia biosand — ~10-yr life, no upkeep. A higher figure isn’t a worse buy: $2.50/person/yr in conflict-torn Goma may save more lives than $0.55 elsewhere. Figures cover hardware and upkeep, not the donated PhD time that designs each system.
For context, global WASH data suggests roughly one life saved per ~1,500 people given safe water. At our costs, that’s a total investment of about $825 (Cambodia, our lowest at ~$0.55/person/yr) to ~$3,750 (DR Congo, our highest at ~$2.50). But 1,500 is only an average: in dire, child-heavy places like Goma, far fewer people are needed to save a life; in moderate-income areas with less-contaminated water, more. Netting those out, the real investment behind a life saved likely lands somewhere around $1,500–$2,500. Browse every project →
Solutions by problem
Every major solution — not just the ones we use — for the three problems we work on. The right tool depends entirely on the water.
| Solution | How it works | Best for | Targets | Approx. cost | Maintenance / life | Key tradeoff |
|---|---|---|---|---|---|---|
| Boiling | Heat to a rolling boil (1 min; 3 at altitude). | Emergency stopgap | Bacteria, viruses, protozoa | ~$75+/person/yr in fuel | None; not durable | Fuel & smoke; no residual |
| Chlorination | Free chlorine disinfects and leaves a residual. | Stored/piped water with a supply chain | Bacteria (6-log), virus (4-log); weak on Crypto | ~$0.66/person/yr; a $1.50 bleach bottle treats ~20,000 gal | Dosing checks; gear 5–10 yr | Taste; fails in turbid water |
| SODIS (solar) | Clear PET bottles in the sun 6 h (2 days if cloudy). | High-sun regions, small volumes | Bacteria, protozoa; weaker on virus | ~$0.30/person/yr | Swap bottles every 6–12 mo | Weather-dependent; ≤2 L |
| Ceramic filters | Water percolates fired clay (often silver-lined). | Household, locally made | 99% bacteria, >99% protozoa; limited virus | ~$3–7/person/yr ($15–50/unit) | Scrub; replace 2–5 yr | Slow flow; breakable |
| Biosand / slow sand | A living bio-layer plus sand traps & digests pathogens. | Durable household/community use | >98% bacteria, >99% protozoa, 85–90% virus | ~$100/unit; ~$0.26–4/person/yr | 10+ yr; swirl-and-dump top sand | Heavy; ~4-week ripening period |
| Hollow-fiber UF (Sawyer) | Gravity 0.1µm membrane — no power. | Dispersed households (our DRC default) | Bacteria (7-log), protozoa (6-log); limited virus | <$0.40 per 1,000 gal; ~$0.11–1.46/person/yr | Syringe backflush; 100,000+ gal life | Won’t remove viruses or chemicals |
| Powered / community UF | Pressurized hollow-fiber at kiosk or school scale. | With power + operator (our PH UF+UV) | Bacteria, virus, protozoa | ~$700 school unit (200+ kids); ~$0.55/person/yr | Membrane 5–15 yr; needs power | Capital cost + skilled upkeep |
| Reverse osmosis | High-pressure membrane rejects salts & metals. | Only when dissolved contaminants demand it | Salts, arsenic, fluoride, viruses | High capex + energy/opex | Membranes; pre-treatment | Wastes water; strips minerals; costly |
| UV disinfection | A UV-C lamp damages microbial DNA. | Clear water + power, point-of-entry | Bacteria, viruses, protozoa | ~$7–69/person/yr | Bulb 5–10 yr; clean the sleeve | Needs power; no residual |
| Coagulation / flocculation | Alum or PAC clumps fine particles to settle out. | Pre-treating turbid surface water | Turbidity; some pathogens & arsenic | Low chemical cost | Dosing & sludge removal | A pre-treatment, not disinfection |
| Rainwater harvesting | Roof catchment + first-flush + storage (a source). | High-rainfall regions | Low-contaminant source water | $2,000–5,000 (storage is >60% of cost) | Clean gutters/tank; 10–20 yr | Seasonal; storage dominates cost |
| Protected wells / boreholes | A sealed wellhead & apron (a source). | Areas with good groundwater | Reduces fecal ingress | Shallow $500–2,000; borehole $15k–40k | Pump upkeep; apron repair | May carry geogenic arsenic/fluoride |
| Arsenic removal | Iron-based adsorption (SONO), coag-filtration, or RO. | Arsenic groundwater (WHO 10µg/L) | Arsenic (III & V) | Iron is cheap; a SONO filter ran 15 yr at 600 ppb | Replace the iron matrix | Needs pH 6–7; As(III) needs oxidation |
| Fluoride removal | Bone char, activated alumina, or the Nalgonda technique. | High-fluoride belts (WHO 1.5 mg/L) | Fluoride | Media + regeneration cost | Periodic media swap | Capacity limits; safe disposal |
Our field principle: low cost protects more people — 99% safe water for 1,000 beats 100% safe water for 50. Pathogens are the default threat (match a filter, chlorine, or UV to a water test); arsenic and fluoride need contaminant-specific media or RO. Figures are approximate, from CWH field assessments cross-checked with WHO, US EPA, and CAWST.
| Solution | How it works | Best for | Targets | Approx. cost | Maintenance / life | Key tradeoff |
|---|---|---|---|---|---|---|
| Activated carbon / biochar | Porous carbon adsorbs mercury (and cyanide); biochar is community-makeable. | Mercury in drinking water | Mercury, cyanide | Low; can be produced locally | Replace spent media | Methylmercury biomagnifies — the real danger |
| Bone char | Hydroxyapatite chemically binds lead & cadmium (also fluoride). | Lead/cadmium in drinking water | Lead, cadmium, fluoride | Cheap; burn bone locally | Replace when saturated | Finite capacity; safe disposal |
| Iron-based adsorption | Iron hydroxides bind arsenic (and some Pb/Cd). | Arsenic-laden water | Arsenic | Iron is cheap and abundant | Replace media | Needs pH ~6–7 |
| Raise pH (dolomite / limestone) | Carbonate raises pH so metals precipitate; adds Ca/Mg. | Acidic, metal-rich water | Zinc & general metals; acidity | Locally abundant (e.g. Ghana) | Replenish media | Only partial for Pb/Cd/Hg |
| Ca/Mg ‘safening agent’ | Dietary calcium/magnesium displaces toxic metals in the body. | Reducing harm at a given exposure | Lowers metal toxicity | Cheap mineral pellets | Slow-dissolving | Mitigates harm; doesn’t remove metal |
| Mercury retorts (source) | Condense & recapture mercury vapor when burning amalgam. | Artisanal gold miners | Reduces mercury released | Cheap per device | Adoption-dependent | Occupational protection only |
| Gravity-borax (source) | Borax + gravity capture gold without any mercury. | Artisanal & small-scale mining | Eliminates mercury use | Cheaper; recovers more gold | Training | Needs local leadership / enforcement |
| AMD neutralization + wetlands | Limestone raises pH; constructed wetlands passively treat. | Acid mine drainage (pH 2.5–4) | Acidity, dissolved metals | Low opex; wetlands need land | Manage metal sludge | Generates sludge to dispose of |
| Cyanide degradation / green chem | Natural degradation, or replace cyanide leaching entirely. | Gold extraction (our Baguio R&D) | Cyanide | R&D-stage | Process change | Substitute still being proven |
| Phytoremediation | Hyperaccumulator plants pull metals into harvestable biomass. | Soils & sediments, slow cleanup | Metals (slowly) | Low cost | Harvest & dispose safely | Slow; don’t route biomass into feed |
| Modified SONO filter — our design | One community-built unit: sand+iron+charcoal (As, Hg) + dolomite (pH, Ca/Mg) + bone char (Pb/Cd) + biochar (Hg, CN). | Multi-metal mining pollution | Arsenic, mercury, lead, cadmium, zinc | Mostly local materials | Needs before/after testing + lifespan est. | A CWH integrated design, in development |
Toxicity roughly follows mercury > arsenic > lead > cadmium > zinc, and acidic mine water makes every metal more soluble. Best solved at the source (mercury-free mining, AMD neutralization) and backstopped with selective adsorption media — which our Modified SONO filter combines into one community-built unit. Spent media and metal sludge must be disposed of safely.
| Solution | How it works | Best for | Targets | Approx. cost | Maintenance / life | Key tradeoff |
|---|---|---|---|---|---|---|
| Diagnosis: sediment P fractionation | Psenner extraction splits sediment phosphorus into releasable vs locked. | Any troubled lake — do this first | Identifies the phosphorus driver | Lab / study cost | One-off study | Needs specialist labs |
| Diagnosis: external vs internal balance | A mass balance shows if P comes from the watershed or the lakebed. | Before choosing any fix | The source of the phosphorus | Study cost | — | Drives the entire strategy |
| Watershed load reduction | Cut external phosphorus: sewage treatment, wetlands, farm BMPs. | Externally-driven eutrophication | Phosphorus, nitrogen | Large; varies widely | Long-term | Political & slow — but the durable fix |
| Alum / PAC | An aluminum floc binds phosphorus and caps the sediment. | Internal (legacy) phosphorus load | Phosphorus (internal) | ~$500–1,000+/ha (public lit.) | Re-dose every 5–15 yr | pH-crash risk; not permanent |
| Phoslock (lanthanum clay) | Lanthanum locks phosphate into an inert mineral. | Internal phosphorus, across pH | Phosphorus | Higher $/ha than alum | Long-lasting | Higher cost per hectare |
| Hypolimnetic aeration | Oxygenates deep water so iron keeps phosphorus bound. | Stratified lakes & reservoirs | Internal P; fish habitat | Capex + power | Ongoing energy | Treats the symptom, not the source |
| Dredging | Physically remove phosphorus-rich or contaminated sediment. | Severe legacy contamination | Phosphorus (removed) | Very high | One-time, disruptive | Cost; spoil disposal; disturbance |
| Biomanipulation | Adjust the fish food-web to suppress algae. | Select shallow lakes | Algae (indirectly) | Low–moderate | Monitoring | Temporary without nutrient cuts |
| HAB early-warning | Models give fishers 2–7 days to harvest before a kill. | Bloom-prone fisheries | Algal-bloom fish kills | Software + sensors | Ongoing | Warns; doesn’t prevent blooms |
| Water-hyacinth phytoremediation | Harvest the fast-growing N/P ‘sponge,’ then turn it into feed. | Nutrient-choked waters | Nitrogen, phosphorus, BOD | Low cost; circular | Frequent harvest | Remove heavy metals first |
| Habitat restoration | Rebuild spawning grounds, mangroves, and riparian buffers. | Degraded fisheries | Ecosystem function | Varies | Long-term | Slow; needs lasting protection |
Restoring a fishery starts with diagnosis: is the phosphorus coming from today’s watershed or legacy lakebed sediment? That answer decides everything — a cheap alum dose can beat an expensive dredge, or it can fail entirely if the watershed keeps loading.
Technical briefs
Full write-ups on the solutions we know best — the chemistry, the design choices, and the numbers. We’re publishing these one at a time.
How hollow-fiber UF and living biosand layers stop cholera & typhoid with no power or chemicals — and exactly where each one falls short.
Read the brief →UF is the core filter — but the right build depends on the water and the community. Prefilters, chlorine cleaning, UV, and activated carbon, and exactly when each one earns its keep.
Read the brief →Removing the two most toxic chemicals from artisanal gold — mercury via borax and retorts, cyanide via a thiosulfate substitute (our Baguio research) — without killing the income communities depend on.
Read the brief →Managing lead, cadmium, copper, and arsenic mobilized by gold mining — using pH adjustment and selective chemistry to lock metals out of water, soil, and food.
Read the brief →Internal vs external phosphorus, and when cheap alum beats an expensive dredge.
Read the brief →Why sponsoring one science or engineering student from a water-poor community — for under $2,000 a year — is the highest-leverage long-term water investment we make.
Read the brief →We publish our mistakes
Honesty about failure is how engineering improves — and how you know you can trust us.
During commissioning of our first Philippine village system, we broke a UV lamp. It cost time and money — and it rewrote our install checklist. Every system since benefits from that mistake.
Across the sector, water systems given away entirely tend not to last — people don’t value free. We now build in a small community contribution, which funds local operators and creates ownership.
In the DRC we deliberately avoided chlorine and complex builds. Gravity membrane filters remove cholera and typhoid without consumables or supply chains — the simplest design that solves the real problem wins.
A full field-notes blog is on the way. Subscribe below to get each new write-up.
External resources
We’re a learning center, not a walled garden. When someone else explains it better, we link to them.
Start here
Drinking water
Heavy metals & mining
Want to go deeper?
Want a full technical brief, a techno-economic write-up, or a capacity statement for due diligence? Just ask — or lend your own expertise.