Emergency & Humanitarian Water Treatment

Free chlorine targets are typically set at 0.5 to 1.0 mg/L at the source to achieve the WHO benchmark residual of 0.2 to 0.5 mg/L at point of use, with higher residuals recommended during active outbreaks or elevated contamination risk. Contact time — the CT product of chlorine concentration and residence time — matters as much as instantaneous dose, and calculations must reflect the expected water quality (turbidity, organics, ammonia) that the disinfectant is working against.

Chlorine speciation shifts with pH, and hypochlorous acid (HOCl) — the effective biocide — drops sharply in efficacy above pH 8.5; source-water pH may require correction ahead of chlorination. Where the source water carries significant organic load, chlorine demand may consume the target dose entirely before it reaches the point of use, driving the need for either higher initial doses or upstream coagulation to reduce demand.

Common process trains combine raw water intake (floating strainer or bank-side pump), chemical coagulation (alum or PAC, dosed on rapid jar-testing), flocculation (mechanical or hydraulic), sedimentation or dissolved air flotation, multi-media filtration (sand, anthracite, sometimes GAC), and membrane polishing where the source water demands it. Ultrafiltration is now standard on higher-spec MWTUs; reverse osmosis where source salinity makes it necessary. Disinfection is typically chlorine (sodium hypochlorite from bulk supply or on-site electrolysis of brine), sometimes UV backed by residual chlorination for pathogen redundancy, or chlorine dioxide where the source water carries higher levels of chlorine-tolerant pathogens.

Every stage is a dosing operation, and field-deployable dosing pumps must operate reliably in extreme temperatures, dusty and salty environments, and often on limited power. Non-electric proportional dosing is a natural fit for the disinfection stage where grid or generator power is unreliable — chlorine can be dosed continuously at proportional rates to source flow without requiring external control power or complex instrumentation.

The design constraints on well-head disinfection in humanitarian contexts are demanding. Zero grid dependence is often required. Simple maintenance by trained field staff — not water treatment engineers — must be practical. Long service intervals with locally sourceable spares matter for sustainability. Compatibility with locally available sodium hypochlorite, which varies substantially in concentration and often arrives partially deteriorated from heat and time, drives equipment selection. And the dose must be proportional to source flow, because hand-pump or gravity flow varies through the day as populations use the water source.

Non-electric proportional dosing pumps meet these constraints better than solenoid or motor-driven alternatives in most field configurations, which is why they are the reference technology for the WASH sector. Proportional dosing — where chlorine flow tracks source flow automatically — eliminates the need for flow measurement and control loop closure, and the absence of electrical power requirements makes the system deployable anywhere water is flowing.

Sodium hypochlorite is the most common disinfectant in emergency and humanitarian contexts — typically 6 to 15% commercial strength, or generated on-site by electrolysis of brine. It degrades with heat and light, and supply chain quality control is a real field issue rather than a specification detail.

Calcium hypochlorite (HTH) in solid form (65 to 70% available chlorine) is preferred in logistics-constrained operations because it has a longer shelf life, ships as a solid, and is dosed as a dissolved solution.

Chlorine dioxide is effective across a wider pH range, effective against Giardia and Cryptosporidium (which are chlorine-tolerant), and does not form trihalomethanes — but requires on-site generation from sodium chlorite plus acid or hypochlorite, which restricts its use to operations with the technical capacity to run the generator safely.

Household-level products — sodium hypochlorite drops, NaDCC tablets, and PUR-type flocculant/disinfectant sachets — cover point-of-use where centralized infrastructure is absent.

Coagulation reduces turbidity before disinfection — chlorine demand and pathogen shielding drop sharply below 1 NTU, so pre-treatment is often a prerequisite for effective residual maintenance. pH adjustment (acidification for some limestone-geology sources, alkalinization for acidic sources) supports effective chlorination.

Iron and manganese removal by oxidation (chlorine or permanganate) and filtration handles high-metal well waters. Where geogenic fluoride exceeds the WHO 1.5 mg/L limit, adsorption on activated alumina or bone char, or precipitation, addresses the specific hazard. Arsenic treatment — coagulation-filtration with ferric or specialized adsorbents — is essential in the many regions where arsenic in groundwater is a chronic public health issue.