When the Borehole Can't Keep Up: Managing Chlorine Decay and Water Safety in Jonglei's Overwhelmed IDP Sites

A hand pump rehabilitated for a village of 400 people does not perform the same way when 3,000 displaced households move in overnight. In Jonglei and Lakes states right now, that is not a hypothetical — it is the operational baseline. Since late 2025, conflict has displaced an estimated 304,000 people across Jonglei State alone, and OCHA reports that more than 70 percent of boreholes and water yards in the affected areas are damaged or non-functional. The communities absorbing displaced populations are drawing water from infrastructure never designed for this density, and the rainy season is pushing turbidity and microbial load higher every week.

For WASH teams managing water points in these conditions, the core challenge is not whether chlorine is being added. It is whether chlorine is still present at the household tap or the jerry can by the time families drink. Free residual chlorine (FRC) decay in overcrowded, high-temperature, high-turbidity settings is faster and more unpredictable than standard dosing tables assume. Getting this wrong in a cholera-active environment is not a compliance gap — it is a transmission risk.

South Sudan's current cholera outbreak has recorded 102,105 cases and 1,662 deaths since it was declared in September 2024, according to OCHA's April 2026 humanitarian update. The outbreak has shifted geographically toward Jonglei and Lakes states, driven precisely by the combination of displacement, flooding, and degraded WASH infrastructure. Understanding why chlorine fails — and how to counter it — is one of the most actionable things a field WASH team can do right now.

Quick answers for field teams:

• The Sphere Handbook minimum is 0.2–0.5 mg/L FRC at the point of delivery; during active cholera transmission, maintain at least 1.0 mg/L FRC at point of use

• Turbidity above 1–2 NTU increases chlorine demand and can neutralise residual within hours — retest at the collection point, not just at the source

• P&G Purifier of Water sachets combine coagulation and disinfection in one step and remain effective in water above 100 NTU where chlorine tablets alone fail

• HTH Calcium Hypochlorite (65–70% available chlorine) is the practical bulk disinfectant for communal water points; a standard 45 kg drum treats approximately 585,000 litres at a 1 mg/L dose

• When IDP population at a water point doubles, recalculate chlorine demand — contact time and dose must increase, not stay fixed

What Population Surges Do to a Water Point's Chlorine Budget

A borehole serving a stabilised IDP population of 500 people at 15 litres per person per day requires 7,500 litres of daily throughput. WASH teams typically calibrate chlorine dosing to achieve 0.5 mg/L FRC at source with enough margin for distribution losses. That calibration becomes irrelevant the moment a displacement wave adds 2,000 more users to the same point.

The problem operates through two mechanisms simultaneously. First, throughput rises sharply, meaning water moves through the distribution system faster and spends less time in contact with chlorine before collection. Contact time is not just a laboratory concept — it is the 30 minutes minimum that WHO specifies at 25°C for sufficient inactivation of bacterial pathogens including Vibrio cholerae. When queue pressure pushes families to fill containers and leave immediately, that contact time is never achieved. Second, increased foot traffic, surface water ingress during the rains, and jerry can cross-contamination raise the chlorine demand of the water at the point of collection. A field team that last measured FRC two weeks ago may be operating on assumptions that have since collapsed.

Research published by the WASH Cluster and cited in a multi-site study across refugee camps in South Sudan, Jordan, and Rwanda (PLOS ONE) found that mean FRC at point of consumption across monitored sites was 0.14 mg/L — below the Sphere lower threshold of 0.2 mg/L. In warmer settings above 30°C — consistent with Jonglei's pre-rain dry season temperatures — FRC decay is further accelerated, and even a compliant source reading can produce a non-compliant collection point result within two to four hours.

The practical implication: in a rapidly expanding IDP site, FRC monitoring frequency must increase from once daily to twice daily or more, and measurement must occur at the most distal collection point, not at the pump head.

Why Turbidity Changes Everything During the Rainy Season

Jonglei's rainy season, which is now beginning, introduces a second variable that fundamentally alters chlorination calculus: turbidity. Surface water flooding, borehole apron deterioration, and run-off ingress into shallow infrastructure drive turbidity in collected water from routine baseline levels of 1–5 NTU to well above 100 NTU during peak rainfall events.

Turbid water does two things to chlorine. Suspended particles carry an organic chlorine demand, consuming available chlorine before it can disinfect. They also physically shield microorganisms — including Vibrio cholerae — from contact with the disinfectant, reducing microbial kill even where a nominal FRC reading is achieved. WHO's drinking water quality guidelines note that turbidity above 1 NTU reduces the reliability of disinfection and that values above 4 NTU make achieving safe residuals at point of use very difficult without prior clarification.

This is where standard chlorine tablet products reach their operational limit. Aquatabs 67mg tablets are effective and appropriate for household use in water of reasonable quality. In flood-turbid water above 30–50 NTU, the chlorine demand of the water can exceed what a single tablet delivers at the recommended 10-litre dosage, and the particle shielding effect reduces bacterial kill to below 4-log. Field teams relying on tablets alone during high-turbidity flooding events are not achieving the protection they believe they are.

The answer is not simply to add more tablets — overdosing chlorine produces unacceptable taste, drives non-compliance, and raises concerns around chlorination by-products. The answer is pre-treatment to remove turbidity before disinfection. For WASH products procurement, this is the operational rationale for stocking P&G Purifier of Water sachets alongside chlorine tablets, not as an alternative but as a complementary tool for high-turbidity conditions.

The Case for P&G Purifier of Water in Flood-Affected Settings

The P&G Purifier of Water sachet works through a two-stage process in a single product. Ferric sulfate acts as a coagulant, aggregating suspended particulates and larger microbes into visible floc that settles to the bottom of a 10-litre container within minutes. Calcium hypochlorite then disinfects the clarified water layer, which is poured through a clean cloth to remove the settled floc. The WHO International Scheme for Evaluating Household Water Treatment Technologies assigns the product a two-star Comprehensive Protection classification, indicating greater than 4-log (99.99%) reduction of bacteria and viruses — including Vibrio cholerae.

Critically, this performance is documented in water with turbidities well above 100 NTU — conditions that would render chlorine-only products partially ineffective. Field studies cited by the WHO's HWTS Knowledge Base found diarrhoeal disease reduction ranging from 16 to over 90 percent across five randomised controlled trials, with the higher results recorded in contexts similar to South Sudan's current conditions: high turbidity, limited household storage infrastructure, and active cholera transmission.

Specialized Logistics Solutions holds exclusive distribution rights for P&G Purifier of Water in South Sudan — a fact that matters for procurement leads. Supply chain continuity in Juba is confirmed, and stock is pre-positioned for rapid dispatch. When programme teams are planning flood-season WASH product requirements, P&G sachets should be budgeted separately from Aquatabs 67mg, with the allocation tied to flood risk assessment at each water point location.

HTH Calcium Hypochlorite at the Community Scale

Household-level treatment addresses the family, but it does not fix the communal water point. Boreholes, hand-dug wells, and surface water collection sites serving hundreds of families require bulk disinfection — and HTH Calcium Hypochlorite in 45 kg drums is the field standard for this task.

HTH granules at 65–70% available chlorine dissolve to produce a stock solution that can be dosed into a water point at scale. A standard 45 kg drum at this concentration treats approximately 585,000 litres of water to achieve 1 mg/L FRC — the threshold recommended for active cholera response per WASH Cluster operational guidance. For a borehole serving 1,500 people at 15 litres per person per day (22,500 litres/day), a single drum provides roughly 26 days of treatment at the cholera-response dose, giving programme teams a predictable stock planning figure.

The most common field error with HTH is calculating dose at the source and assuming that reading holds at the point of collection. In high-heat, high-turbidity conditions, FRC can drop from 1.0 mg/L to below detectable levels within 2–4 hours in a jerry can stored in direct sunlight. This decay is not a product failure — it reflects the chlorine demand of the water and the ambient conditions. The operational response is to raise the source-point FRC target to 2 mg/L during active cholera response (per WASH Cluster guidance), verify at the collection point, and increase monitoring frequency.

For programmes managing multiple water points across Jonglei or Lakes counties, pumps and equipment procurement should include adequate testing kit stocks — ORP meters and DPD-based colorimetric test kits — as part of any HTH order. A chlorinated water point with no functioning test kit is operationally blind.

Integrating the Full Response: What Field Teams Should Do Now

The rainy season in Jonglei has begun. Flooding and IDP population movements will continue to stress water infrastructure through October. WASH teams operating in Jonglei, Upper Nile, and Lakes states should take three concrete steps before the peak rainfall months intensify.

First, rebaseline chlorine dosing at every water point where population has grown since the last calibration. Do not assume last season's dose is adequate. Document current population served, daily throughput, and turbidity range, then recalculate demand and verify with point-of-collection FRC tests at the beginning and end of the distribution day.

Second, pre-position a turbidity-responsive treatment option alongside standard chlorine tablets. Aquatabs 67mg remain appropriate for water with turbidity below 5 NTU. For flood events or sites drawing from surface water, P&G Purifier of Water sachets are the field-appropriate product. Stocking both — and training community health workers to select between them based on a simple visual turbidity assessment — is low-cost insurance against a treatment failure during peak rainfall.

Third, ensure HTH drum stock at all communal water points is sized for the cholera-response dose, not the standard Sphere dose. Given that South Sudan's outbreak remains active with cases still being reported in Jonglei as recently as April 2026, the lower 0.5 mg/L target is not appropriate for these sites. Plan at 1.0–2.0 mg/L FRC at source, verify at collection point, and adjust.

For programme managers also planning physical infrastructure, warehouses and shelters from Hallgruppen's modular range can provide covered water distribution points and hygiene promotion spaces that protect both water quality and community health worker safety during the rains.

What This Means for Your Programme

The cholera situation in Jonglei and Lakes is not a background risk — it is an active outbreak in a geography where more than 70 percent of water infrastructure is damaged or destroyed, population has tripled or more at functioning water points, and the rainy season is adding turbidity and surface-water contamination every week. Chlorination is the intervention, but chlorination as a fixed routine without population- and turbidity-adjusted dosing is not sufficient protection.

The evidence base for what works is clear: FRC monitoring at point of collection rather than point of source, turbidity-adapted treatment products, and bulk chlorination targets calibrated to cholera-active settings. The products to execute on this evidence are available and in-country.

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. Contact the team at sales@maji-safi.org.

Frequently Asked Questions

What free residual chlorine level should I target at a water point in a cholera-active area?

The Sphere Handbook sets a baseline of 0.2–0.5 mg/L FRC at the point of delivery under normal conditions. During active cholera transmission, WASH Cluster operational guidance recommends maintaining at least 1.0 mg/L FRC at the point of use, which typically requires targeting 1.0–2.0 mg/L at the source to account for decay in transit and storage. Verify with a DPD test kit at the most distal collection point, not only at the pump head.

Why do Aquatabs stop working in turbid flood water?

Aquatabs 67mg tablets release chlorine that disinfects dissolved pathogens. When water turbidity rises above 5–10 NTU, suspended particles carry organic matter that consumes available chlorine before it can disinfect, and particles can physically shield bacteria from the disinfectant. Above 30–50 NTU in typical flood conditions, chlorine demand can exceed what a single tablet delivers at the 10-litre dose, making bacterial kill unreliable. Pre-clarification with a coagulant-flocculant product like P&G Purifier of Water restores disinfection effectiveness.

How do I calculate how many HTH drums my programme needs for a cholera response?

A 45 kg drum of HTH at 65–70% available chlorine treats approximately 585,000 litres of water to a 1 mg/L FRC dose. Multiply your daily throughput (people served × 15 L/person/day minimum) by 30 days to get monthly volume, then divide by 585,000 to get drum requirement per water point per month. For multiple water points or populations above Sphere minimum allocation, recalculate with actual consumption figures.

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

Use P&G Purifier of Water when source water turbidity exceeds 5 NTU, when water is drawn from surface sources during flooding, or when a visual turbidity check shows visible cloudiness. Use Aquatabs when water has been clarified or when source turbidity is low. Both products should be stocked at flood-risk sites. P&G sachets are also appropriate for households receiving water trucking deliveries that may have been sitting in tanks for extended periods.

How often should FRC be tested at a water point serving a large IDP population?

At water points serving more than 500 people, or at any point where population has increased rapidly due to displacement, UNHCR and WASH Cluster field guidance recommends FRC testing at least twice per day — at the start and end of the main distribution period — and always at the point of collection, not only at the source. Where test kit supplies allow, additional mid-day checks during peak rainfall events or following any population influx are strongly recommended.