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Water Treatment Dosing Calculator: Breakpoint Chlorination, Product Quantity and Pump Rate

Dosing water with only the target free chlorine residual in mind quietly under-treats it, because added chlorine is first consumed by demand, ammonia, organics and reducing agents, before any stable free residual can actually form. This chlorine demand calculator applies proper breakpoint logic, total dose equals demand plus target residual and then converts that chlorine mass into a real product quantity based on your actual source. Liquid sodium hypochlorite, calcium hypochlorite bleaching powder and chlorine gas each carry very different available-chlorine strengths, so the same disinfection target needs very different physical amounts of each. As a genuine dosing pump rate calculator, its Continuous Flow mode turns a flow rate and target dose into a pump feed rate for inline treatment systems rather than just a one-off batch tank dose and an optional cost estimate multiplies product quantity by chemical price.

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How to Use

Step 1: Choose Batch Tank or Continuous Flow

• Select Batch Tank if you’re dosing a fixed volume of water once, a tank, bucket or reservoir. Select Continuous Flow if you’re running an inline treatment system that needs an ongoing dosing-pump feed rate.
• In Batch Tank mode, enter your Water Volume in litres. In Continuous Flow mode, enter your Flow Rate in litres per hour instead.

Step 2: Set your chlorine demand and target residual

• Enter the Chlorine Demand (mg/L) of your water, how much chlorine gets consumed by ammonia, organics, and other reducing agents before any stable residual appears. This figure normally comes from a jar test or known water quality data.
• Enter your Target Free Residual (mg/L), the actual disinfecting chlorine level you want left over after demand is satisfied, WHO guidance suggests 0.2 to 0.5 mg/L for drinking water maintenance.
• Note the reminder below these fields: total dose equals demand plus residual, since the dose must first satisfy demand before any stable free residual can appear at all.

Step 3: Select your chlorine source

• Select your Source Type: Liquid Sodium Hypochlorite (~12%), Bleaching Powder / Ca-Hypochlorite (~30%), or Chlorine Gas (100%). This pre-fills the typical percent available chlorine for that source.
• Check the % Available Chlorine field that fills in automatically, and replace it with your actual measured or labelled strength whenever you have it, since real hypochlorite and bleaching powder batches lose strength over time and vary between suppliers.
• If you selected a liquid source, a Liquid Density field appears, enter it in g/mL, 1.2 is a common default, to convert the required mass into an actual volume to dose.

Step 4: Add cost, if you want it

• Under Cost (optional), enter your Chemical Cost (per kg). In Batch Tank mode this gives a one-time cost; in Continuous Flow mode it gives a cost per hour instead. Leave this blank to skip.

Step 5: Calculate and read your result

• Tap Calculate Dose. In Batch Tank mode, the result shows the total chlorine mass required, the actual product quantity to add (in grams for powder/gas, or millilitres for liquid) and the cost if entered. In Continuous Flow mode, the result additionally shows the dosing-pump feed rate needed to maintain your target dose continuously at your entered flow rate.

Step 6: Export

• Use Print / PDF for a clean printable copy or Copy to paste the figures into your treatment log.

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Key Features

• Breakpoint chlorination logic, total dose equals chlorine demand plus target free residual, not just the residual alone
• Source-based product conversion, Liquid Sodium Hypochlorite, Bleaching Powder/Ca-Hypochlorite or Chlorine Gas, each with a different typical available-chlorine strength
• Always-editable % available chlorine, since real product batches vary and lose strength over time
• Batch Tank and Continuous Flow modes, the latter converting flow rate and dose directly into a dosing-pump feed rate for inline systems
• Liquid density conversion, turning required chlorine mass into an actual volume to dose for liquid sources
• Optional cost estimate, one-time for batch, per-hour for continuous flow
• A clear reminder that effective disinfection also depends on contact time (CT value), not dose alone
• Export as PDF or copy the result.

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Formula / Logic Used

Breakpoint Chlorine Dose

$$Dose\ (mg/L) = Chlorine\ Demand + Target\ Free\ Residual$$

Chlorine Mass Required

$$Chlorine\ Mass\ (mg) = Dose\ (mg/L) \times Volume\ (L)$$

Product Quantity from Source Strength

$$Product\ Quantity = \frac{Chlorine\ Mass}{\% Available\ Chlorine / 100}$$

For a liquid source, this mass is further converted to volume using the product’s density:

$$Volume\ (mL) = \frac{Product\ Mass\ (g)}{Density\ (g/mL)}$$

Continuous-Flow Dosing Pump Rate

$$Pump\ Rate = Flow\ Rate\ (L/hr) \times \frac{Dose\ (mg/L)}{\% Available\ Chlorine \times Density\ Factor}$$

The chlorine mass needed per hour is calculated the same way as the batch dose, just scaled to the hourly flow rate instead of a fixed volume.

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Who Should Use This Tool

Water treatment plant operators and site engineers sizing chlorine dosing for a tank, reservoir, or continuous inline treatment system. Also useful for diploma and B.Tech Environmental and Civil Engineering students learning breakpoint chlorination and available-chlorine product conversion for their coursework.

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Frequently Asked Questions (FAQs)

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Related Tools

• BOD/COD Estimator – check organic load before dosing, since it directly affects chlorine demand
• Rainwater Harvesting Tank Size Calculator – size the storage tank you’re now dosing
• Molarity / Normality Calculator – for chemical solution concentration calculations in the same treatment process