Water Tank Disinfection Calculator 💧 Site Guideline
🧊 Water Tank Compartment Volume
⚖️ Chlorine Disinfectants Required Amount & Recorded Site Preparation Report
0 kg (Kilograms)
This report is recorded with on-site photo & confirmed by Licensed Plumber ©️ Zhilong Team.
📸 Water Tank Cleaning Visual Guide Checklist | Zhilong Team
Step-by-step Visual Checklist for PUB SS 636 Standard Compliance
1. Structural Overview (Before Cleaning)
Site Photo + Overlay
Systematically document the initial condition inside the water tank before cleaning begins.
Key Focus: Take clear photos of any scale, sludge, sediment, or bio-fouling on the Ceiling, Wall, and Floor.
2. Hazard & Safety Compliance (LOTO)
PUB SS 636:2018
Record compliance with Lock-out/Tag-out (LOTO) safety procedures at the power isolator.
Key Focus: Photo proof showing LOTO installed on the power isolator with proper danger warning signage attached.
3. High-Pressure Jetting & Scrubbing (or) by Manually
Action Photo
Clean internal surfaces of the water tank using high-pressure jet washers / scrubbers.
Key Focus: Action photo showing direct pressure washing on tank wall, ceiling, and floor surfaces.
4. Chlorine Dosing Workflow Visual
MOS
Systematic step-by-step chemical pre-mixing process.
⚠️ Warning: Pre-dissolve Calcium Hypochlorite powder in a bucket/drum and allow white lime sediment to settle. DO NOT pour dry powder directly into the water tank.
5. Live Dosing & Refilling Process
Action Photo
Pour the clear strained chlorine solution into the water tank gradually while refilling with fresh potable water.
Key Focus: Action photo showing clear liquid chlorine solution being poured into the tank through the access cover.
6. Hanna Colorimeter Water Test Result
Meter Screen Close-up 📸 (Proof to PUB)
Document water quality testing (Total / Residual Chlorine) using a digital colorimeter after disinfection.
Key Focus: Close-up photo showing reading value on meter screen (50/200 ppm dosage or Residual Chlorine < 2.0 ppm) along with timestamp.
* Standard Target: 50 mg/L (ppm) for 24-hr contact time (SS 636 Clause A.1.2.3 & A.1.2.5)
* Emergency / Urgent or Single Tank Target: 200 mg/L (ppm) for 2-hr contact time (SS 636 Clause A.1.2.12 & A.1.2.13)
* Important: Powder chemical must be pre-dissolved in water. DO NOT pour the chlorine mixture into the tank immediately after stirring. Wait a few minutes for the white lime sediment to settle at the bottom of the bucket/drum. Pour ONLY the clear liquid on top into the tank. ⚠️ Do NOT dump dry powder directly into the tank (Clause A.1.2.2).
* Emergency / Urgent or Single Tank Target: 200 mg/L (ppm) for 2-hr contact time (SS 636 Clause A.1.2.12 & A.1.2.13)
* Important: Powder chemical must be pre-dissolved in water. DO NOT pour the chlorine mixture into the tank immediately after stirring. Wait a few minutes for the white lime sediment to settle at the bottom of the bucket/drum. Pour ONLY the clear liquid on top into the tank. ⚠️ Do NOT dump dry powder directly into the tank (Clause A.1.2.2).
PUB SS 636 Compliance Guidelines
Q: What is the standard dosage for routine water tank disinfection?
A: 50 mg/L (50 ppm) of free chlorine for a minimum contact/soak time of 24 hours (SS 636:2018 Clause A.1.2.3 & A.1.2.5).
Q: What if the water tank cannot be isolated for 24 hours?
A: Clause A.1.2.12 & A.1.2.13 allows an emergency dosage of 200 ppm free chlorine kept in the tank for at least 2 hours before complete flushing.
Q: How should Calcium Hypochlorite powder be safely applied?
A: Direct dumping in dry powder form is strictly prohibited (Clause A.1.2.2). It must be pre-dissolved in water, strained of lime sediment, and fed gradually during tank refilling.
Q: What is the acceptable residual chlorine limit for water sampling?
A: After flushing chlorinated water and refilling with fresh potable water, total residual chlorine must be below 2.0 mg/L (2.0 ppm) to pass PUB laboratory water test standards.
Q: What electrical safety steps must be taken before entering the tank?
A: Turn off main power to the tank, put a Lock-out/Tag-out card at the switchboard, and test exposed metal parts with a contactless voltage meter before and after work (Clause A.1.1.3).
Q: What notices must be displayed before starting tank cleaning?
A: Inform consumers in advance and place clear warning signboards showing "Water Tank Cleaning in Progress" near the work area (Clause A.1.1.5).
Q: How to protect water pipes during cleaning and chemical dosing?
A: All outlet pipes inside the tank must be tightly covered/closed to stop dirt, sludge, or high-chlorine water from flowing into user tap lines (Clause A.1.1.14 & A.1.2.4).
Q: What tools can be used for cleaning inside the water tank?
A: Use smooth tools with no sharp edges to avoid damaging the tank lining. Tools must be dedicated for drinking water tanks ONLY and disinfected before use (Clause A.1.1.13).
Q: How to clean and disinfect the tank roof and upper walls?
A: Apply 200 mg/L (200 ppm) chlorine solution to the ceiling/roof and wall surfaces above the overflow line by spraying or brushing, and leave for at least 30 minutes (Clause A.1.1.16).
Q: What are the health & hygiene rules for workers entering the tank?
A: Workers must have medical certificates / vaccinations for water-borne diseases (typhoid, cholera, hepatitis), must NOT feel unwell, and must wash and disinfect themselves before entering (Clause A.1.1.10 & A.1.1.11).
Q: Who is authorized to take water samples from the tank?
A: Water samples must be taken by a Licensed Plumber (LP) or personnel from a SAC-SINGLAS-accredited laboratory (Clause A.1.2.7 & A.1.2.8).
Q: Where should water samples be taken if the tank has no sampling tap?
A: Samples shall be taken from the bottom of the tank using an appropriate sampling device (Clause A.1.2.6).
Q: What analyses must be performed on the water samples?
A: Samples must be sent to a SAC-SINGLAS-accredited lab for bacteriological, chemical, and heavy metal leaching analyses (Clause A.1.2.6 & A.1.2.15).
Q: What security measures are required for sample transportation?
A: Samples must be sealed, marked by the owner/representative, and escorted to the lab. Any samples with broken seals shall be rejected (Clause A.1.2.7 & A.1.2.8).
Q: When can the water tank be put back into service after cleaning?
A: Only after satisfactory test reports are obtained from the accredited lab, and all downfeed / distributing pipes are thoroughly flushed (Clause A.1.2.8).
Q: What action is required if the lab test reports are unsatisfactory?
A: Disinfection procedure must be carried out again completely from the beginning (Clause A.1.2.9 & A.1.2.15).
Q: What administrative step is required after work completion?
A: The LP must notify the Authority on prescribed forms accompanied by the accredited laboratory water sample test reports within the stipulated period (Clause A.1.2.11).
Q: Can other chemical disinfectants besides chlorine be used?
A: The use of any other chemical or procedure is allowed ONLY if specifically approved by the Authority (Clause A.1.2.16).
Hanna Total Chlorine Testing Procedure For Single Tank or Urgent Short-Time Chlorination Needed Water Tank Case
🛠️ Required Testing Equipment:
- Hanna Total Chlorine Handheld Colorimeter (Checker)
- Glass Cuvettes with Caps (2 clean glass vials: Cuvette A & Cuvette B)
- Total Chlorine DPD Reagent Powder Packets
- Lint-free Microfiber Cloth (For wiping glass cuvettes)
📋 Step-by-Step Hanna Chlorine Kit Testing Method:
-
Step 1: Zero Calibration (Cuvette A)
Press the power button once to turn on the Checker (screen displays "Add C.1" and "Press"). Fill Cuvette A with 10 mL sample water, cap it, and thoroughly wipe glass exterior with a microfiber cloth. Insert Cuvette A into Checker, close lid, and press button. Zero calibration is complete when screen displays "Add C.2" and "Press". -
Step 2: Reagent Preparation (Cuvette B)
Fill Cuvette B with 10 mL sample water and add 1 packet of Total Chlorine DPD Reagent Powder. Cap Cuvette B and gently swirl for 2 minutes until powder completely dissolves.* Caution: Do NOT shake vigorously to prevent air bubbles, which distort light sensors and cause inaccurate ppm readings. -
Step 3: Countdown Timer & Reading
Wipe Cuvette B glass exterior clean and insert into the Checker (replacing Cuvette A). Close lid.
CRITICAL STEP: PRESS AND HOLD the button until the 2-minute 30-second countdown timer appears on screen, then release.
When countdown finishes, the meter will automatically display the precise Total Chlorine concentration in mg/L (ppm). -
Step 4: Photo Evidence & Time Recording 📸
Take a clear photo showing the Hanna Checker screen reading (ppm) as photo proof.* IMPORTANT TIME GAP: For Single Tank (200 ppm) short-time chlorination, the timestamp on this Hanna test kit result photo MUST be at least 2 hours LATER than the photo showing 200 ppm chlorine dosing during fresh potable water filling.
💡 Licensed Plumber & On-Site Team Quality Assurance Tips: ℹ️ Hanna Total Chlorine Test Kit To Be Conducted At Single Tank ⚠️ ONLY After Minimum 2 hrs Contact-Time with 200 PPM Chlorinated Water Remaining in tank and ⚠️ After final Drain-Out the Chlorinated Water from tank ■
- Glass Cuvette Surface: Any fingerprints, or water droplets on the glass exterior will block light transmission, causing artificially high ppm readings.
- Air Bubble Elimination: Gently tap the glass cuvette if micro-bubbles cling to the inner walls before inserting into the Checker.
- Built-in Timer Usage: Always use the 2:30 minutes timed measurement mode (Press & Hold) to ensure complete chemical reaction of DPD powder for lab-grade accuracy.
🧪 Chlorine Disinfectant Types in Singapore Market (PUB SS 636 Compliance)
🇸🇬 SINGAPORE CHEMICAL MARKET SUPPLY OVERVIEW
1. Powder / Granules Form (Calcium Hypochlorite)
Chemical Formula: Ca(ClO)₂ | Active Strength: 65% – 70%
Market Overview: Most widely used chemical in Singapore for commercial and residential water tank chlorination due to long shelf life and cost-efficiency.
Local Suppliers/Brands: HTH Chlorine Granules, Sinopex 70%, Nankai 70% (Supplied by Kimic Chemitech, Masda Chemical, Aik Moh, GB Chemicals).
⚠️ PUB Standard: Must be pre-dissolved in a bucket/drum and strained of insoluble white lime sediment before feeding into the water tank.
Market Overview: Most widely used chemical in Singapore for commercial and residential water tank chlorination due to long shelf life and cost-efficiency.
Local Suppliers/Brands: HTH Chlorine Granules, Sinopex 70%, Nankai 70% (Supplied by Kimic Chemitech, Masda Chemical, Aik Moh, GB Chemicals).
⚠️ PUB Standard: Must be pre-dissolved in a bucket/drum and strained of insoluble white lime sediment before feeding into the water tank.
2. Liquid Form (Sodium Hypochlorite Solution)
Chemical Formula: NaClO | Active Strength: 10% – 12% (Industrial Grade)
Market Overview: Preferred for quick jobs because it leaves no solid sediment and mixes instantly with water.
Local Suppliers/Brands: Industrial Sodium Hypochlorite Solution 10%/12% (Supplied by GB Chemicals, Chemtrade Asia, Innova Corporate, Polaris Chemical).
💡 Direct Pouring: Can be fed directly into the water stream through the access hatch while refilling fresh water.
Market Overview: Preferred for quick jobs because it leaves no solid sediment and mixes instantly with water.
Local Suppliers/Brands: Industrial Sodium Hypochlorite Solution 10%/12% (Supplied by GB Chemicals, Chemtrade Asia, Innova Corporate, Polaris Chemical).
💡 Direct Pouring: Can be fed directly into the water stream through the access hatch while refilling fresh water.
3. Tablet / Effervescent Form (NaDCC)
Chemical Name: Sodium Dichloroisocyanurate (NaDCC) / Troclosene Sodium
Market Overview: Pre-measured exact dosage tablets. Highly convenient for small water storage tanks, single-compartment systems, or remote site testing.
Local Suppliers/Brands: Klorsept, Aquatabs (Agis Medical Supplies / Kersia Medentech Singapore).
Market Overview: Pre-measured exact dosage tablets. Highly convenient for small water storage tanks, single-compartment systems, or remote site testing.
Local Suppliers/Brands: Klorsept, Aquatabs (Agis Medical Supplies / Kersia Medentech Singapore).
📊 PUB SS 636:2018 Disinfection Criteria Summary
| Disinfection Type | Target Concentration | Required Contact Time | Final Potable Limit |
|---|---|---|---|
| Standard Routine | 50 ppm (mg/L) | 24 Hours | < 2.0 ppm |
| Urgent / Single Tank | 200 ppm (mg/L) | 2 Hours (Min.) | < 2.0 ppm |
⚪ Technical Guideline: NaDCC Tablet Form Disinfection (PUB SS 636 Compliance)
✅ Is Tablet Form (NaDCC) PUB SS 636:2018 Compliant?
YES, COMPLIANT. PUB SS 636 requires a specified concentration of Free Available Chlorine (50 ppm or 200 ppm) in the water system. NaDCC (Sodium Dichloroisocyanurate) effervescent tablets release active Hypochlorous Acid (HOCl) to meet this exact requirement.
🎯 Key Advantages of Tablet Form:
- 🎯 Precise Dosing: Pre-measured active chlorine per tablet (e.g., 2.5g or 5g active chlorine) eliminates site weighing errors.
- 📦 Easy Transport & Handling: Compact and lightweight compared to heavy liquid drums or bulky powder tubs.
- ✨ 100% Insoluble Sediment Free: Unlike Calcium Hypochlorite powder, NaDCC tablets dissolve completely without leaving lime sludge.
- 🛡️ Enhanced Safety: Minimal fumes, no chemical splashing, and reduced risk of skin/clothing corrosion during preparation.
🏠 Practical Application: Domestic vs Commercial Water Tanks
🏠 Highly Preferred for: Single Water Compartment Tanks, Small Domestic Water Tanks, or Condominium Overhead Smaller Tanks where quick setup and space efficiency are required.
🏭 Commercial Large Tanks Note: For very large capacity tanks (> 100 m³), hundreds of tablets would be required. In such high-volume cases, Calcium Hypochlorite powder or Liquid Sodium Hypochlorite is usually preferred for cost efficiency and faster dissolving speed.
💡 On-Site Quality Assurance Checklist for Tablet Disinfection:
- Pre-Dissolving Rule: Always drop tablets into a dedicated bucket/drum first to let them effervesce completely before pouring solution into the main tank.
- Lab Sampling Validation: Ensure final flushing reduces total residual chlorine below 2.0 ppm before submitting water samples to SAC-SINGLAS lab for physical / chemical & microbiological analysis.
⏰ Local Date & Time: --