Free tool
Chlorine Calculator for Drinking Water
Calculate the exact dose of sodium hypochlorite, coagulants and pH adjustment for your treatment system. Formulas with specific gravity correction and a check against NOM-127-SSA1-2021, Mexico’s drinking water standard.
- NOM-127 built in
- Specific gravity corrected
- Batch and continuous flow
Dosage Calculator
Calculate the chemicals your water system needs
Tank or cistern capacity
Measured free chlorine residual. For untreated water, use 0
NOM-127-SSA1-2021 (Mexico’s drinking water standard): 0.2–1.5 mg/L free chlorine residual
Select the type and concentration
Flow rate of the system to be treated
Total dose = chlorine demand + target residual
Select the type and concentration
Used to calculate daily consumption
Result · dosage by volume
Product required
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Active chlorine required
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Show formula used
Active chlorine (g) = Volume (L) × ΔConcentration (mg/L) / 1000
Product (mL) = Active chlorine (g) / (Concentration (%) × 10 × Specific gravity) × 1000
* Reference estimate. Specific gravity (SG) values correspond to fresh solutions. Stored product may have a lower concentration (~80% of nominal). Verify with laboratory analysis.
Is this for a hotel, condominium or business? We confirm the dose with a drinking water analysis (NOM-127) at a laboratory accredited by EMA (Mexico’s accreditation entity).
Get a water test quoteResult · continuous dosing
Feed rate
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Equivalent
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Daily consumption
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Monthly consumption
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Show formula used
Rate (L/h) = Flow rate (m³/h) × Dose (mg/L) / (Conc. (%) × 10 × SG)
* Reference estimate. Allow for a 20% degradation factor for hypochlorite stored more than 30 days.
Want the dosing to run automatically? We quote the dosing pump, the hypochlorite and free chlorine residual monitoring.
Request a dosing quoteWater flow rate to be treated
Measured with a turbidimeter. Guide: <5 clear, 5-50 turbid, >50 very turbid
Select based on availability
Used to calculate daily consumption
Result
Recommended dose
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Hourly consumption
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Daily consumption
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* The optimal dose must be determined by a jar test. This calculation is an initial estimate based on turbidity.
Total volume to adjust
Measured with a pH meter or test strip
NOM-127-SSA1-2021 (Mexico’s drinking water standard): pH 6.5–8.5
If unknown, use 150 (typical value in Quintana Roo)
Result
Recommended chemical
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Approximate amount
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* pH adjustment depends on multiple factors (temperature, dissolved solids, CO₂). This calculation is a rough estimate.
Measured at the end of the contact tank
Actual time from dosing point to the first user. Recommended minimum: 30 min
pH affects chlorine effectiveness
Average water temperature in Cancún: 25-30°C
Result — CT verification
Calculated CT value
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Required CT (3-log)
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Compliance
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* Reference CT values based on the EPA Surface Water Treatment Rule for 3-log Giardia inactivation with free chlorine.
Important: These calculators provide reference estimates based on standard engineering formulas. For precise dosing in production systems, consult a specialist and run laboratory analysis.Request free technical advice.
Where is the water for?
My home · rooftop tank or cistern
What you need to chlorinate at home
- Sodium hypochlorite 13%, 20 L jugDelivery in Cancún, Puerto Morelos and Playa del CarmenFree quote
- Chlorine and pH analyzerTo check the resultFree quote
Our online store is in Spanish.
Hotel, condominium or business
NOM-127 requires more than calculating the chlorine
We dose, measure and document the chlorine in your cistern, and test the water for COFEPRIS, Mexico’s federal health regulator.
Frequently asked questions
See the formula used
Active chlorine (g) = Volume (L) × ΔConcentration (mg/L) / 1000. Product (mL) = Active chlorine (g) / (Concentration (%) × 10 × Specific gravity) × 1000. For continuous dosing: Rate (L/h) = Flow (m³/h) × Dose (mg/L) / (Concentration (%) × 10 × SG).
How much chlorine do you need for 1,000 liters of water?
To leave 1 mg/L of chlorine in 1,000 liters of unchlorinated water: 15.3 mL of 6% household bleach or 6.6 mL of 13% sodium hypochlorite. If the water comes from a tanker truck or an untreated well, use 2 mg/L (30.6 mL at 6% or 13.1 mL at 13%), wait 30 minutes and measure: free chlorine residual should end up between 0.2 and 1.5 mg/L, as NOM-127-SSA1-2021 (Mexico’s drinking water standard) requires. Sodium hypochlorite 13%, 20 L jug (store in Spanish) →
How much chlorine should I add to a 1,100-liter rooftop tank?
For a 1,100-liter rooftop tank (tinaco) with unchlorinated water and a target of 1.0 mg/L: 16.8 mL of 6% household bleach or 7.2 mL of 13% sodium hypochlorite. In the calculator: 1100 liters, 0 mg/L current, 1.0 mg/L target and the product you will use. Sodium hypochlorite 13%, 20 L jug (store in Spanish) →
How many drops of chlorine per liter of water?
To disinfect drinking water at home, the health guidelines of Mexico City and Veracruz call for 2 drops of commercial bleach (6% sodium hypochlorite) per liter and 20 to 30 minutes of standing time with the container covered. With 13% hypochlorite, 1 drop per liter is enough. For rooftop tanks and cisterns, measuring in milliliters with the calculator is more accurate. DPD free chlorine test kit (store in Spanish) →
How many chlorine tablets go in a 1,100-liter rooftop tank?
200 g trichlor tablets are for pools: each carries about 180 g of chlorine, more than a hundred times what a 1,100-liter tank needs (1.1 g for 1 mg/L), and they leave stabilizer in the water. For drinking water, use liquid hypochlorite measured with the calculator; if you prefer tablets, make sure the label says they are for drinking water and follow the manufacturer’s dose. Sodium hypochlorite 13%, 20 L jug (store in Spanish) →
How often should I chlorinate my cistern?
Check the chlorine residual daily and dose as needed. In systems without continuous flow (static cisterns), disinfect at least every 24–48 hours, since chlorine is naturally consumed by organic matter, temperature and sunlight. Chlorine and pH analyzer (store in Spanish) →
Which sodium hypochlorite concentration should I use?
For household use, 6% sodium hypochlorite (commercial bleach) is the most accessible. Treatment plants use 10–13% for efficiency and cost. Calcium hypochlorite (65–70%) is a solid and is preferred where longer storage is needed or in remote areas. The one in our store is 13%. Sodium hypochlorite 13%, 20 L jug (store in Spanish) →
What is the difference between free chlorine and total chlorine?
Free chlorine (free chlorine residual) is the portion of chlorine available for disinfection. Total chlorine is free chlorine plus combined chlorine (chloramines, formed when chlorine reacts with ammonia). NOM-127-SSA1-2021 requires free chlorine residual between 0.2 and 1.5 mg/L in drinking water. DPD free chlorine test kit (store in Spanish) →
Why does the calculator include specific gravity?
Sodium hypochlorite is denser than water (SG 1.09–1.17 depending on concentration). Without the specific gravity correction, the actual volume of product needed is underestimated by 9–17%. Our calculator applies the SG correction automatically for each concentration.
What is the CT value and why does it matter?
The CT value is the disinfectant concentration (C, in mg/L) multiplied by the contact time (T, in minutes). It is the standard indicator that disinfection is effective. An adequate CT ensures the inactivation of pathogens such as Giardia. For example, at pH 7.5 and 25 °C, a minimum CT of 25 mg·min/L is required.
Chlorine dosing table for drinking water
Approximate amount of sodium hypochlorite needed to reach 1.0 mg/L of chlorine in untreated water, corrected for specific gravity.
| Water volume | NaOCl 6% | NaOCl 10% | NaOCl 13% | Typical use |
|---|---|---|---|---|
| 200 L | 3.1 mL | 1.8 mL | 1.3 mL | Small rooftop tank |
| 450 L | 6.9 mL | 3.9 mL | 3.0 mL | Compact rooftop tank |
| 1,000 L | 15.3 mL | 8.8 mL | 6.6 mL | Rooftop tank or 1 m³ tank |
| 1,100 L | 16.8 mL | 9.6 mL | 7.2 mL | Standard rooftop tank |
| 2,500 L | 38.2 mL | 21.9 mL | 16.4 mL | Residential cistern |
| 5,000 L | 76.5 mL | 43.9 mL | 32.8 mL | Large cistern |
| 10,000 L | 152.9 mL | 87.7 mL | 65.6 mL | Industrial tank |
| 50,000 L | 764.5 mL | 438.6 mL | 327.8 mL | Municipal reservoir |
* Values for a 1.0 mg/L dose in water with no prior chlorine residual. For other doses, use the calculator above. Formula: mL = (V × D) / (C% × 10 × SG) × 1000. SG: 6% = 1.09, 10% = 1.14, 13% = 1.17.
Technical reference
Chlorine dosing: key concepts
The standard formula for calculating the amount of chlorine product is:
Batch mode: Product (mL) = V (L) × ΔC (mg/L) / (Conc% × 10 × SG) × 1000
Continuous flow: Rate (L/h) = Q (m³/h) × D (mg/L) / (Conc% × 10 × SG)
Factors that affect the dose:
- Chlorine demand: organic matter, ammonia and contaminants that consume chlorine before a free residual forms
- Target residual: 0.2–1.5 mg/L for drinking water (NOM-127-SSA1-2021)
- Contact time: at least 30 minutes for effective disinfection
- Specific gravity: NaOCl is denser than water (SG 1.09–1.17), so less volume is needed than the uncorrected calculation gives
- Degradation: hypochlorite loses strength with time, temperature and light. Use 80% of the nominal strength for product stored longer than 30 days
For pools, NOM-245-SSA1-2010 (Mexico’s pool water standard) requires 1.0 to 5.0 mg/L of free chlorine residual.
Coagulant dosing
Coagulants remove turbidity, color and suspended solids. Factors to consider:
- Initial turbidity: higher turbidity means a higher dose
- Water pH: each coagulant has an optimal pH range for floc formation
- Alkalinity: affects buffering capacity and the alkalinity the coagulant consumes
- Temperature: cold water needs a higher dose and a longer flocculation time
The optimal dose should always be determined with a laboratory jar test.
pH adjustment and CT value
Optimal pH for different treatment processes:
- Chlorine disinfection: 7.0–7.5 (hypochlorous acid is most effective)
- Coagulation with aluminum sulfate (alum): 6.0–7.5
- Coagulation with PAC: 6.5–8.5
- Boiler water: 10.5–11.5 (corrosion protection)
- NOM-127 drinking water: 6.5–8.5
The CT value (concentration × time) is the key indicator of effective disinfection. At lower pH and higher temperature, a lower CT is needed because hypochlorous acid (HOCl) is more effective.
Adjust pH gradually: add 50% of the calculated amount, mix, measure and repeat if needed.
Need technical advice for your site?
Our engineers can design the right dosing program for your operation