Water tools
Cooling tower blowdown & cycles calculator
Estimate evaporation, blowdown, and make-up water for an evaporative cooling tower from its recirculation rate, temperature range, and cycles of concentration — and see how much water higher cycles save.
How it works
The water balance on a cooling tower is Make-up = Evaporation + Blowdown + Drift, and the cycles of concentration N set how far the dissolved solids concentrate before bleed:
Evaporation is estimated as E ≈ 0.00085 × recirculation × range(°F), a widely used rule of thumb (range in °F is the °C range × 1.8). Blowdown follows from the cycles: B = E / (N − 1) − Drift. Make-up is the sum of all three losses.
Cycles of concentration equal the ratio of a conserved species in the circulating water to the make-up (for example N = conductivity_recirc / conductivity_makeup). Raising cycles cuts both make-up and blowdown, until scaling or corrosion limits set the ceiling — which is where treatment chemistry and the saturation index come in.
Evaporation and drift are estimates; confirm evaporation against a site heat balance and use the drift rate from the eliminator data sheet.
Related reading
These calculators use standard published formulas and are provided for preliminary engineering guidance. Confirm against measured data and vendor projections before design. Model your full water matrix in Nepti or post your project to compare provider proposals.