Addition of fluoride (as HF, NaF, or fluorosilicic acid H₂SiF₆) to drinking water mains at precise dosing levels to meet regulatory fluoride targets of 0.7–1.5 mg/L (milligrams per litre).
Coefficient of Variation (CoV) ≤0.05 at residual analyser location. Injection ratio extremely low (<0.005% v/v) — one of the most demanding dilution duties. Wide turndown (10:1) in distribution systems must maintain uniform dosing at minimum flow.
Preferred MOC: FRP or PVDF mandatory for fluorosilicic acid (H₂SiF₆) — highly corrosive to metals. 316SS or FRP for sodium fluoride (NaF). Injection quill in PVDF or Hastelloy C-276.
Injection quill with PVDF tip essential — neat fluorosilicic acid contacts nozzle tip. Multi-port nozzle for DN>200. pH analyser minimum 3D downstream. Regulatory compliance: PHE (UK), EPA (US), WHO guidelines.