Use of public water supply fluoride concentration as an indicator of population exposure to fluoride in England 1995-2015

Background: Public health monitoring of Community Water Fluoridation (CWF) schemes requires estimates of exposure to fluoride in public water supplies (PWS). We aimed to use routine data to estimate population exposure to PWS-fluoride in England and to determine whether PWS-fluoride exposure from 2005-2015 could be used as a proxy for exposure for 1995-2004, when fluoride concentration data that could be linked to population health data were unavailable. 
Methods: Annual mean water supply zone PWS-fluoride concentrations were calculated from monitoring data for 1995-2015, stratified by fluoridation scheme-flagging. We allocated annual 2005-15 mean PWS-fluoride concentrations to small area boundaries to describe population exposure within five concentration categories (<0.1mg/L to ≥0.7mg/L). We compared zone-level 1995-2004 and 2005-15 mean PWS-fluoride concentrations using Spearman correlation.
Results: 72% of the population received PWS with <0.2mg/L fluoride and 10% with ≥0.7mg/L. Grand-mean 1995-2004 and 2005-15 fluoride concentrations were similar (0.11mg/L (SD 0.12), and 0.11mg/L (SD 0.12), respectively) and highly correlated (coefficient 0.93) if un-fluoridated, but differed (1995-2004 0.74mg/L (SD 0.22), 2005-15 0.78mg/L (SD 0.16)) and correlated weakly (coefficient 0.31) if fluoridated. 
Conclusions: We estimated categorised population exposure to PWS-fluoride concentrations for public health monitoring. 2005-2015 fluoride concentrations approximate those in 1995-2004 but with a greater risk of misclassification in fluoridation schemes.