The reference dose: about 2 mg/L
Polyphosphate works by a threshold effect: a very small, sub-stoichiometric dose disrupts the nucleation of calcium carbonate — you do not need to bind all the calcium to slow scaling. The useful range for drinking water is roughly 1 to 5 mg/L:
- 1 mg/L — often enough to protect a network against carbonate scaling.
- 3 mg/L — typical engineering value.
- 5 mg/L — the high end of many proportional dosers for potable water.
As a sensible default we take 2 mg/L. The upside: polyphosphate conditions the water (anti-scale, anti-corrosion, Fe/Mn sequestration) with no salt, no waste water and no electricity, unlike a softener.
The dosing formulas (proportional doser)
For a proportional doser, the material balance is simple:
Mass per day (g/day) = Q (L/day) × D (mg/L) ÷ 1000
Specific consumption (g/m³) = D (mg/L)
Cartridge life (days) = M₀ (g) ÷ (Q × D ÷ 1000)
- Q — water flow rate to be treated
- D — target dose (mg/L)
- M₀ — initial mass of media in the cartridge (g)
Household example at 2 mg/L
Consumption and cartridge life at the 2 mg/L reference dose, for a 250 g and a 140 g refill:
| Flow (L/day) | Consumption (g/day) | Consumption (g/year) | Life 250 g (days) | Life 140 g (days) |
|---|---|---|---|---|
| 100 | 0.2 | 73 | 1250 | 700 |
| 200 | 0.4 | 146 | 625 | 350 |
| 400 | 0.8 | 292 | 312 | 175 |
| 800 | 1.6 | 584 | 156 | 87 |
Calculation assumption: constant target dose of 2 mg/L. Actual figures vary with hardness, temperature and water usage.
Industrial scenarios
When the industrial flow is expressed in m³/h, the useful format is:
g/h = Q (m³/h) × D (mg/L)
kg/day = 24 × Q × D ÷ 1000
| Flow (m³/h) | g/h | kg/day |
|---|---|---|
| 1 | 2 | 0.048 |
| 5 | 10 | 0.24 |
| 10 | 20 | 0.48 |
What changes the real dose
Polyphosphate works across a wide range of conditions. Its effect is at its maximum up to about 40 °C; beyond that it keeps protecting, simply less optimally — common formulations are rated up to 75–80 °C, and some silico-polyphosphates up to 100 °C. It gives its best on moderately hard water; on harder water, a stronger dose or a silico-polyphosphate formulation keeps protection effective. For optimal, continuous protection, replace the cartridge regularly so the dose stays steady.
Need help sizing your installation? Contact our technical team or explore our anti-scale solutions.