Scaling Water Treatment in Cholera Response: When to Move from Household Sachets to Centralized Chlorination

A WASH programme manager coordinating response across three IDP sites in North Kivu faces a specific decision within the first 72 hours: distribute point-of-use treatment sachets to household level, establish centralized chlorination at the water distribution point, or run both in parallel. The answer depends on site population, water source type, supply chain access, and case incidence — and getting it wrong in an active cholera outbreak costs lives.

The stakes are acute right now. UNICEF has described the DRC cholera outbreak as the worst in 25 years, with 5.3 million people requiring emergency water and sanitation support. In parts of North Kivu, displaced populations survive on as little as 6.3 litres of water per day — less than half the Sphere minimum of 15 litres per person per day. A Continental Cholera Emergency Preparedness and Response Plan covering the period through early 2026 remains active across multiple African states. South Sudan's WASH Cluster is simultaneously managing cholera response in Duk and Uror counties, where IOM has rehabilitated hand pumps and reached thousands of households with hygiene messaging.

The scale of the response demands that field teams understand not just what products to deploy, but at what stage each tool performs best. Misapplying point-of-use products to populations of 10,000 creates a logistics bottleneck. Deploying bulk chlorination without adequate field testing creates a false sense of safety. This post sets out the operational logic for scaling water treatment through a cholera response.

Quick answers for field teams:

• Sphere minimum is 15 litres per person per day in emergencies; during cholera response, water needs increase due to oral rehydration, handwashing, and surface cleaning.

• Free residual chlorine (FRC) target at point of use is 0.2–0.5 mg/L under normal conditions; raise to 1.0 mg/L at point of distribution during active cholera transmission.

• P&G Purifier of Water sachets (4g per 10L) are WHO-classified as Comprehensive Protection — effective against bacteria including Vibrio cholerae, viruses, and protozoa, even in highly turbid water.

• HTH Calcium Hypochlorite (65–70% available chlorine) is the standard for bulk disinfection of tanks, trucked water, and distribution points.

• Run household-level and centralized treatment in parallel when populations exceed 5,000 and water sources are mixed (hand pumps plus trucked water).

Why the Treatment Decision Is Not Straightforward

The instinct in acute-phase cholera response is to move immediately to bulk treatment — chlorinate the water at source and assume protection flows downstream. This works reliably in a camp with a single piped or trucked supply. It fails when households collect water from multiple sources: a rehabilitated hand pump, a surface river, a neighbour's jerrycan. Centralized treatment at one distribution point does not protect a household that collects half its water elsewhere.

A systematic review published in PLOS Medicine found that WASH interventions — particularly point-of-use water treatment — significantly reduce cholera transmission when applied consistently at household level. The same evidence base shows that free residual chlorine decays during storage, particularly in warm climates, meaning water treated at a central point can arrive at the household with FRC below the protective threshold. In high-density displacement settings where storage times are long, this decay matters.

The practical implication: centralized chlorination protects the volume distributed at the point; point-of-use treatment protects the volume actually consumed. In a cholera outbreak, you need both layers operating simultaneously at sites above a certain population threshold. The decision point for most WASH coordinators is around 2,000–3,000 people, where the logistics of sachet distribution at scale begin to align with the operational investment required for a centralized chlorination system.

Household-Level Products: Where Sachets and Tablets Fit

Point-of-use water treatment tools fall into two categories that have distinct operational profiles. Aquatabs 67mg sodium dichloroisocyanurate (NaDCC) tablets provide pre-measured chlorine dosing at household level. Each tablet treats 20 litres of water, requires no mixing equipment, and is stable in field conditions. Aquatabs are used by UN agencies, NGOs, and peacekeeping forces globally, and independent studies confirm 99.9999% removal of Vibrio cholerae. They are the appropriate tool for household distribution when water sources are low to medium turbidity and the primary gap is chlorine disinfection.

P&G Purifier of Water sachets address a different problem. Each 4g sachet treats 10 litres and combines ferric sulphate (a coagulant/flocculant) with calcium hypochlorite (a disinfectant). The flocculant stage removes suspended particulates and larger microbes before the disinfection stage acts. This makes sachets effective in highly turbid water — surface sources, river water, flood water — where tablets alone would be consumed by organic matter before reaching a protective FRC. The WHO International Scheme to Evaluate Household Water Treatment Technologies classifies P&G Purifier of Water as Comprehensive Protection against bacteria (including Vibrio cholerae and Salmonella), viruses (including Rotavirus and Poliovirus), and protozoa (including Cryptosporidium and Giardia), making it one of the few point-of-use products to meet all three microbial targets.

During South Sudan's cholera response, over 3.28 million P&G sachets were deployed to support programme operations. For field teams working from the WASH products portfolio, the product selection logic is: use Aquatabs 67mg where water turbidity is low and source consistency is predictable; use P&G sachets where turbidity is high, sources are mixed, or the water requires both clarification and disinfection before consumption.

The critical operational constraint for both products is behaviour. A randomized controlled trial in Dhaka found that Aquatabs usage fell by 50% after intensive behavioral promotion visits concluded. Point-of-use treatment that depends on consistent household action is vulnerable to compliance decay. This is not a reason to avoid these products; it is a reason to build hygiene promotion into every distribution cycle and to not rely on POU treatment alone as a population scales.

Centralized Chlorination: HTH at Distribution Points and Tanks

When site population crosses 3,000 and a reliable central water supply exists — whether trucked, pumped from a borehole, or drawn from a river through a treatment system — centralized chlorination with HTH Calcium Hypochlorite becomes the more efficient system. HTH granules at 65–70% available chlorine are designed for bulk disinfection of large volumes: water tanks, trucking tankers, distribution points, and swimming-pool scale storage.

The dosing target under normal conditions is 0.5 mg/L FRC at the distribution point, with water arriving at the household retaining at least 0.2 mg/L. During active cholera transmission, the Sphere Handbook and WHO guidance both specify raising the distribution point FRC target to 1.0 mg/L to account for recontamination risk during collection, handling, and storage. Field teams must measure FRC at both the distribution point and the point of use — not just at the source — to verify that protective levels are maintained through the chain.

IRC's response in DRC included the establishment of 10 centralized chlorination points and a water trucking system with a 90 m³ per day capacity. UNICEF set up hundreds of additional chlorination and oral rehydration points across DRC's active hotspots. These systems protect populations at scale in a way that household-level distribution cannot match alone, but they require trained operators, ongoing chemical supply, and water quality testing equipment.

For field procurement, HTH Calcium Hypochlorite drums are available through Specialized Logistics Solutions (SLS), which holds pre-positioned stock in Juba and Kampala. Teams coordinating both trucked water operations and pump systems — including Aussie Pumps dewatering units and Multiquip pumps — can integrate bulk chemical supply with equipment procurement through a single in-country supplier, reducing lead times during acute response phases.

The Parallel Approach: Running Both Systems in Active Outbreak Conditions

The most effective cholera response in large displacement settings runs centralized and household-level treatment simultaneously, with each layer addressing a distinct risk. Centralized chlorination protects the primary distributed supply. Household sachets or tablets protect against recontamination during transport, storage, and use. Hygiene promotion — soap, handwashing stations, safe storage vessels — addresses the behaviours that determine whether treated water stays treated.

UNICEF's guidance on cholera response specifies that water trucking programmes must include FRC testing at the point of collection, hygiene promotion messaging at every distribution point, and coordination with the health cluster on cholera case mapping. The mapping component is operationally significant: case distribution data identifies which collection points and community zones carry the highest transmission risk, allowing WASH teams to target intensified chlorination and household distribution rather than spreading resources evenly across a site.

In practice, this parallel approach requires field stock of both bulk chlorine (HTH) and household treatment products (Aquatabs and P&G sachets), alongside jerrycans, FRC test kits, and — in sites where hand pump rehabilitation is part of the response — pump repair equipment. South Sudan's WASH Cluster response in Uror County combined hand pump rehabilitation with hygiene messaging to 2,200 households, demonstrating the integrated model in operation. For teams building procurement plans, the WASH products portfolio provides the full range of treatment options — from sachets and tablets through to bulk chemical supply — and the pumps and equipment range covers the hardware needed to move and distribute water at scale.

Monitoring FRC Across the Treatment Chain

Free residual chlorine testing is not optional in a cholera response — it is the mechanism that confirms whether treatment is working. FRC must be measured at three points: immediately after dosing (source or treatment point), at the distribution point, and at the point of use (in a household storage container). Gaps between these measurements reveal where protection is being lost.

WHO emergency technical guidance specifies that turbidity above 5 NTU significantly reduces chlorine efficacy, which is why turbid water sources require either pre-sedimentation, coagulation/flocculation (the function the ferric sulphate in P&G sachets performs), or filtration before disinfection. Teams that skip turbidity measurement and dose HTH directly into turbid trucked water will see FRC test results that appear adequate at the distribution point but drop below protective levels within minutes as chlorine is consumed by organic matter.

Common field failures include: under-dosing HTH to extend supply, failing to re-dose water stored overnight in tanks, distributing tablets without confirming households have appropriate container volumes, and running promotion campaigns that assume literacy. Each of these failures is recoverable once identified through systematic FRC testing and case surveillance cross-referencing.

What This Means for Your Programme

The current DRC and South Sudan cholera context requires field teams to move fast without cutting corners on water quality verification. The treatment layer that matters most is the one closest to consumption — which is why household-level tools remain essential even when centralized systems are operating. The decision to add P&G sachets or Aquatabs to a response where HTH chlorination is already running is almost always the right one, because the two systems protect against different failure points in the same chain.

Specialized Logistics Solutions (SLS) holds pre-positioned stock of P&G Purifier of Water sachets, Aquatabs 67mg tablets, and HTH Calcium Hypochlorite drums in Juba and Kampala, available for rapid dispatch. With 35+ years of operational history in South Sudan, Uganda, Kenya, and DRC, and exclusive South Sudan distribution rights for P&G Purifier of Water, SLS is UNGM-registered (Vendor No. 380716) and routinely supplies IOM, UNMISS, WHO, UNICEF, IRC, Concern Worldwide, MEDAIR, and ForAfrika. Contact the team at sales@maji-safi.org.

Frequently Asked Questions

What FRC level should I target during an active cholera outbreak?

Sphere and WHO guidance specifies a minimum of 1.0 mg/L free residual chlorine at the point of distribution during active cholera transmission — double the 0.5 mg/L standard for non-outbreak conditions. At the point of use (inside household storage containers), the minimum is 0.2 mg/L. Measure at both points; the gap tells you where recontamination is occurring.

When should I use P&G Purifier of Water sachets instead of Aquatabs?

Use P&G sachets when water sources are highly turbid — surface water, river water, or flood water — because the ferric sulphate flocculant removes suspended particles and microbes before the calcium hypochlorite disinfects. Aquatabs work best in low-to-medium turbidity water where clarification is not needed. In practice, sachets are the better default when source quality is variable or unknown.

Can I run centralized HTH chlorination and household-level sachet distribution at the same site?

Yes — this is the recommended approach for sites above 3,000 people with mixed water sources. Centralized treatment at the distribution point protects the primary supply volume. Household sachets or tablets protect against recontamination during transport and storage. The two systems address different failure points and are not redundant.

How much water does the Sphere standard require per person per day in a cholera response?

The Sphere minimum is 15 litres per person per day. During cholera response, this requirement increases because patients need additional water for oral rehydration, caregivers need water for handwashing, and surfaces require cleaning. WASH coordinators should plan for 20–25 litres per person per day in active cholera response settings, particularly in treatment facility catchment areas.

How do I calculate the HTH dose needed for a water trucking operation?

For HTH at 65–70% available chlorine, a general field calculation for a target FRC of 1.0 mg/L is approximately 1.5–2.0 grams of granules per 1,000 litres of water, adjusting upward for turbidity or long storage times. Always verify with FRC testing after 30 minutes of contact time before distribution. Contact the SLS team at sales@maji-safi.org for product-specific dosing tables.