WaterCalculator

Water Treatment Calculators

22 tools for softening, filtering and treating water — sizing and salt use, filter life, reverse osmosis performance, UV disinfection, and the chemistry behind hardness, scaling and corrosion. Each runs on the recognised standard formula, with the working shown.

Sarah Bennett, MS Curated and reviewed by Sarah Bennett, MS, Water Quality & Sustainability Specialist.

Softening & hardness

Water Softener Size CalculatorSoftener size (grain capacity) for your household and hardness. Water Softener Salt UsageSalt used per regeneration cycle. Water Softener CapacityGrain capacity between regenerations. Softener Regeneration FrequencyHow often your softener should regenerate. Grains Per GallonWater hardness expressed in grains per gallon. Hardness PPM to GPGConvert hardness between ppm/mg-L and gpg.

Filtration & sizing

Iron Filter SizingSize an iron filter for your water's iron level. Carbon Filter SizingSize a carbon filter for flow rate and contact time. Sediment Filter LifeExpected service life of a sediment filter. Filter Replacement ScheduleWhen to replace a whole-house water filter.

Reverse osmosis

Reverse Osmosis SizingSize an RO system for household demand. RO Rejection RateShare of dissolved solids an RO membrane rejects. RO Recovery RateShare of feed water recovered as permeate.

UV disinfection

UV Dose CalculatorUV disinfection dose from flow and intensity. UV TransmittanceWater's UV transmittance for disinfection sizing.

Conductivity & TDS

Conductivity to TDSConvert conductivity into total dissolved solids. EC to PPM CalculatorConvert electrical conductivity to parts per million.

Dosing & dilution

Dilution CalculatorDilute a stock solution to a target concentration. Stock Solution CalculatorPrepare a stock solution at a target concentration.

Scaling & stability indices

Alkalinity CalculatorWater's alkalinity from titration or bicarbonate levels. Langelier Saturation IndexA water's scaling or corrosive tendency. Ryznar Stability IndexA water's scaling and corrosion stability index.

About our treatment calculators

These tools are built on the standards water treatment runs on — grains-per-gallon hardness math, EPA/AWWA guidance for filtration and reverse osmosis sizing, and the Langelier and Ryznar saturation indices for scaling and corrosion tendency. Every figure is verified against the live calculator, and each page lists its sources. For the full detail of how we build and check them, see our methodology.

Browse other categories

ScienceDensity, weight, heat and properties. FlowPipe flow, velocity, friction loss. PressureHead, PSI, depth and losses. UsageHousehold use, footprints, savings. CostBills, rates and running costs. PumpsSizing, head, horsepower, NPSH. DrainageSlopes, drain sizing, stormwater.