Water treatment calculators on this site are 7 tools that turn plant measurements into design and control numbers, from the Langelier Saturation Index and cooling-tower blowdown to chemical feed rates, CT values, coupon corrosion rates, glycol freeze points and unit conversions, plus 2 quote tools for treatment programs and chemicals. Each one shows its equation and the public source behind it, so which calculator answers which question at your plant?
The tools serve operators, engineers and procurement staff in industrial, municipal and utility systems, with metric and US units in parallel. The calculators sit beside the reference on water treatment chemicals, so each result links to the chemistry that explains it.
Every equation and constant behind these tools is checked against public primary sources (eCFR, US DOE, operator-certification formula sheets, ASTM and handbook tables). See our methodology and fact-checking process.
What Is a Water Treatment Calculator?#
A water treatment calculator is an online tool that applies a published equation, such as the Langelier Saturation Index or the pounds formula, to plant measurements and returns a number with its unit and basis.
The result is an estimate from the inputs entered. It does not replace a jar test, the certificate of analysis of the delivered product or a calibrated pump drawdown.
All Water Treatment Calculators in One Table#
The 7 water treatment calculators below cover water balance, cooling-tower water use, chemical feed, disinfection, corrosion, glycol loops and unit conversion, and each row gives its question, inputs, outputs and equation.
The table compares the 7 calculators side by side.
| # | Calculator | Question it answers | Inputs (metric and US) | Outputs | Equation | Source | Systems | Status |
|---|---|---|---|---|---|---|---|---|
| 1 | Langelier Saturation Index calculator (LSI, RSI, PSI) | Will this water scale or corrode at its temperature? | pH; temperature °C (°F); TDS mg/L; calcium hardness and total alkalinity, mg/L as CaCO3 | pHs, LSI, RSI, PSI | LSI = pH - pHs; RSI = 2 pHs - pH; PSI = 2 pHs - pHeq, pHeq = 1.465 log10(total alkalinity) + 4.54; pHs by the Carrier formula | Hach method 8073; Veolia handbook ch. 25; Puckorius and Brooke 1991 | cooling, boiler make-up, drinking-water distribution | in preparation |
| 2 | cooling tower water balance calculator | How much make-up and blowdown at a cycles target? | recirculation m³/h (gpm); range °C (°F); evaporation factor; cycles; drift % | evaporation, blowdown, make-up | E = 0.001 x RR (gpm) x ΔT (°F) x F; metric E = RR (m³/h) x ΔT (°C) x 0.0018 x F; BD = E / (C - 1); MU = E x C / (C - 1) | Veolia handbook ch. 31; US DOE FEMP BMP 10 | open recirculating cooling | in preparation |
| 3 | chemical dosage and feed rate calculator | How many kg/d, lb/day, L/h or pump % for a dose in mg/L? | flow (m³/h, m³/d, L/s, gpm, MGD); dose mg/L and basis; strength (wt %, g/L, trade %); density or SG; pump capacity; mode (continuous, slug, blowdown-paced) | kg/d, lb/day, L/h, mL/min, pump setting % | lb/day = mg/L x MGD x 8.34 / purity; kg/d = mg/L x m³/d / 1,000; mL/min = m³/d x mg/L / (density x strength x 1,440) | Florida DEP formula table 2014; EOCP Math for Operators | every dosed system | in preparation |
| 4 | CT value calculator | Does residual times contact time meet the required inactivation? | disinfectant (free chlorine, chloramine, chlorine dioxide, ozone); residual mg/L; contact time min; temperature °C (°F); pH | CT achieved vs CT99.9 required, mg·min/L | CT = C x T | 40 CFR 141.2 (definition); 40 CFR 141.74 (CT tables) | utility drinking water | in preparation |
| 5 | corrosion rate calculator | What is the coupon corrosion rate? | weight loss mg; alloy density g/cm³; coupon area cm² (in²); exposure h | mpy, mm/y | mpy = 534 x W / (D x A x T) with A in in²; mm/y = 87.6 x W / (D x A x T) with A in cm²; 1 mpy = 0.0254 mm/y | ASTM D2688-23 method | cooling, closed loops, boiler condensate | in preparation |
| 6 | glycol freeze point and dilution calculator | What strength protects the loop, and how much glycol to add or drain? | glycol type (EG, PG); present and desired strength, wt %; system volume L (gal); lowest ambient °C (°F) | freeze point; volume to add or drain | add A = V (D - P) / (100 - P); drain A = V (P - D) / P | manufacturer freeze-point and dilution tables (wt % basis) | chilled-water and glycol loops | in preparation |
| 7 | water treatment unit converter | What is this value in another unit? | value and unit (mg/L, ppm, gpg, German, French or English degree, meq/L, %; m³/h, gpm, MGD; kg/d, lb/day) | converted value with basis | 1 gpg = 17.1 mg/L as CaCO3; 1 °dH = 17.848; 1 °fH = 10; 1 English degree = 14.3 mg/L as CaCO3; mg/L as CaCO3 x 0.02 = meq/L; 1 MGD = 3,785 m³/d; 1 gpm = 0.2271 m³/h | Florida DEP formula table; Veolia handbook ch. 40; Hach | every system | in preparation |
Quote Tools: Program Quote and Chemical Quote#
The 2 quote tools route a request to independent providers and suppliers: the program quote for a treatment program with service, and the chemical quote for supply of a named chemical by grade, strength and packaging.
For a program quote, have make-up and blowdown meter readings and conductivity, the cycles target and the chemical cost per 1,000 gal (3.785 m³), the inputs US DOE FEMP lists for cooling towers. For a chemical quote, have the certificate of analysis, the AWWA standard and the NSF/ANSI/CAN 60 certification with its maximum use level in mg/L.
The table compares the 2 quote tools.
| # | Quote tool | Use it for | What the form asks | Have ready | Status |
|---|---|---|---|---|---|
| 1 | water treatment program quote | a cooling, boiler, closed-loop, membrane, wastewater or drinking-water program with service | site type; system; size (tonnage, steam rate, flow); location; current provider; problem | make-up and blowdown meter readings; make-up and blowdown conductivity; cycles target; chemical cost per 1,000 gal (3.785 m³); system volumes in m³ (gal); chiller tonnage | in preparation |
| 2 | request quotes for water treatment chemicals | supply of a named chemical | chemical; grade or strength; NSF/ANSI/CAN 60 need; volume and packaging (drum, IBC, bulk); delivery country | certificate of analysis requirement; AWWA standard; NSF/ANSI/CAN 60 certificate with the listed maximum use level in mg/L | in preparation |
Which Water Treatment Calculator Do You Need?#
The right water treatment calculator follows from the plant question: scale or corrosion, cooling-tower water use, chemical feed, disinfection contact time, loop freeze protection or a unit that needs converting.
The table matches each plant question to a calculator.
| Plant question | System | Calculator | Then read |
|---|---|---|---|
| Will this water scale or corrode? | cooling, boiler make-up, distribution | Langelier Saturation Index calculator | Langelier Saturation Index |
| How fast is metal corroding? | cooling, closed loops | corrosion rate calculator | corrosion coupons |
| How much make-up and blowdown? | open cooling towers | cooling tower water balance calculator | cycles of concentration; cooling tower blowdown |
| How much chemical per day, and what pump setting? | every dosed system | chemical dosage and feed rate calculator | chemical dosing pumps |
| Is the contact time enough? | utility drinking water | CT value calculator | CT values for disinfection |
| Will the loop freeze, and how much glycol to add? | chilled-water and glycol loops | glycol freeze point and dilution calculator | glycol system treatment |
| What is this value in another unit? | every system | water treatment unit converter | water hardness |
| Which provider can run the program? | every system | water treatment program quote | water treatment companies |
Will the water scale or corrode? Saturation index and corrosion rate#
The LSI calculator predicts whether water will scale or corrode: a cooling-tower water at pH 8.2, 35 °C (95 °F), 1,500 mg/L TDS, 400 mg/L calcium and 200 mg/L alkalinity as CaCO3 returns an LSI of +1.29, an RSI of 5.63 and a PSI of 5.92. On the Carrier interpretation, 0.5 to 2 reads as scale forming and below -0.5 as seriously corrosive. The Ryznar and Puckorius scales are worked through under the Langelier Saturation Index.
Measured corrosion comes from corrosion coupons: the corrosion rate calculator turns weight loss into mpy and mm/y, and UK HSE guidance (HSG274 Part 1, 2nd edition 2024) sets carbon steel generally below 5 mpy (0.13 mm/y), preferably below 2 mpy (0.05 mm/y).
How much water does a cooling tower use? Cycles, blowdown and make-up#
A cooling tower's water use follows from evaporation and cycles: blowdown equals evaporation divided by (cycles minus one), and make-up equals evaporation times cycles divided by (cycles minus one) (Veolia Water Technologies Handbook, chapter 31). In its worked table, 50,000 gpm (11,355 m³/h) at a 20 °F (11.1 °C) range and 4 cycles needs 1,330 gpm (302 m³/h) of make-up and 333 gpm (75.6 m³/h) of blowdown.
Raising cycles from 3 to 6 cuts make-up by 20 % and blowdown by 50 % (US DOE FEMP). The calculator checks the make-up to blowdown flow ratio against the conductivity ratio used to control cooling tower blowdown, and scale and silica limits on cycles of concentration are explained separately.
How much chemical should be fed? Dose, feed rate and pump setting#
The chemical dosage calculator turns a dose in mg/L into a feed rate: kg/d equals mg/L times m³/d divided by 1,000, and lb/day equals mg/L times MGD times 8.34 divided by purity (Florida DEP formula table, 2014). Worked example (EOCP Math for Operators): 8.5 mg/L of NaOCl into 2,500 m³/d (0.66 MGD) needs 21.25 kg/d (46.8 lb/day) as NaOCl, or 148.8 L/d (39.3 gal/d) of 12.0 % solution at 1.19 kg/L.
Cooling inhibitor feed is paced on blowdown: lb/day equals product ppm times blowdown gpm times 0.012 (kg/d: times blowdown m³/h times 0.024). For chemical dosing pumps, the setting starts at 100 % stroke length.
Is the disinfection contact time enough? CT values#
The CT value calculator multiplies the residual disinfectant concentration in mg/L by the contact time in minutes (40 CFR 141.2) and compares the product with the CT99.9 Giardia values of 40 CFR 141.74. At 10 °C (50 °F) the reference values are:
- Free chlorine: 104 mg·min/L at pH 7.0 and a residual of 0.4 mg/L or less.
- Chloramine: 1,850 mg·min/L.
- Chlorine dioxide: 23 mg·min/L.
- Ozone: 1.4 mg·min/L.
Chloramine needs about 18 times the CT of free chlorine at pH 7 and 10 °C, so the disinfectant sets the contact basin; see CT values for disinfection.
Will a closed loop freeze? Glycol freeze point and dilution#
A glycol freeze point calculator reads the freeze point of ethylene or propylene glycol at a given strength: 30 wt % propylene glycol freezes at -12.7 °C (9.2 °F) and 30 wt % ethylene glycol at -14.1 °C (6.7 °F), in manufacturer freeze-point tables.
Closed loops run 25 to 60 % inhibited glycol, with a freeze point at least 3 °C (5 °F) below the lowest ambient; the tool returns the volume to add or drain on a wt % basis. Glycol system treatment and testing are covered under closed loop water treatment.
Which unit is this? mg/L, ppm, gpg and degrees of hardness#
Water treatment units convert by fixed constants: 1 gpg equals 17.1 mg/L as CaCO3, 1 German degree 17.848 mg/L, and 1 French degree 10 mg/L.
The ppm unit equals mg/L only near a density of 1; the unit converter handles units of water hardness and concentration.
The table lists the converter's constants.
| From | To | Factor | Basis note |
|---|---|---|---|
| 1 gpg | mg/L as CaCO3 | 17.1 | hardness |
| 1 German degree (°dH) | mg/L as CaCO3 | 17.848 | = 10 mg/L CaO |
| 1 French degree (°fH) | mg/L as CaCO3 | 10 | hardness |
| 1 English (Clark) degree | mg/L as CaCO3 | 14.3 | hardness |
| mg/L as CaCO3 | meq/L | x 0.02 | equivalent weight 50.0 |
| 1 % | mg/L | 10,000 | dilute solutions |
| ppm | mg/L | x solution density | equal only near density 1 |
| 1 US gal | L | 3.785 | 8.34 lb of water |
| 1 gpm | m³/h | 0.2271 | calculated |
| 1 MGD | m³/d | 3,785 | calculated |
Source: Florida DEP Formula/Conversion Table (rev. 2014-02-24) and published hardness tables.
How Are the Calculators Built? Units, Dose Basis and Sources#
Every calculator on this site follows 3 build rules: metric and US units side by side, a named basis for every dose and concentration, and an equation taken from a public source with its validity limits shown.
Metric and US units side by side#
Each input accepts metric and US customary units, converted with fixed constants: 1 US gallon is 3.785 L and weighs 8.34 lb, 1 gpm is 0.2271 m³/h and 1 % is 10,000 mg/L.
Every dose names its basis#
The same liquid alum feed reads as three different doses: 100 gpd of liquid alum into 10 MGD is 13.3 ppm as product, 6.45 ppm as dry alum and 1.26 ppm as Al2O3, so every calculator asks for the basis before it returns a number. The worked example (NJAWWA) uses SG 1.33, a 48.5 % solution and 9.5 % Al2O3. Hypochlorite trade % is g/L of available chlorine divided by 10: 12.5 trade % is 125 g/L, about 11.2 wt % NaOCl.
Validity limits and what a result does not replace#
Each equation has a validity range, stated beside the result.
- Puckorius Scaling Index: applies up to 93 °C (199 °F).
- Evaporation factor: runs 0.75 to 1.0, about 0.6 in very cold weather.
- Biocide holding-time index: fits recirculating systems only, not once-through systems or volatile biocides.
- Coupon corrosion rate: valid only with exposure time, alloy and a pitting note.
Questions About Water Treatment Calculators#
These answers cover cost, scope and where the chemistry and the program review behind each calculator sit.
Are the water treatment calculators free?#
Yes: every water treatment calculator on this site is free to use, and each result shows the equation and source it came from.
Do the calculators cover swimming pools or household water?#
No: the calculators default to industrial, municipal and utility inputs, such as cooling-tower, boiler and drinking-water plant values, and do not give pool, spa or household dosing.
Is there a boiler blowdown calculator?#
Boiler blowdown is calculated as a percent of feedwater, not of steam: percent blowdown equals feedwater chloride divided by boiler-water chloride times 100, and cycles equal 100 divided by that percent.
The full method is set out under boiler blowdown calculation and control.
Where is the chemistry behind each calculator explained?#
Each calculator links to its concept page, and all of them sit in one section of water treatment chemistry concepts covering scaling, corrosion, disinfection and coagulation.
To read them in one place, browse the water treatment chemistry concepts.
Who reviews a treatment program after the calculation?#
A water treatment program provider reviews the program behind a calculated number, such as a cycles target or an inhibitor feed rate, with site tests and service visits.
How to compare water treatment companies is explained in the provider guide.