Every fact on fernrain.com comes from one of these. Checked 27 Oct 2026.
- US EPA — National Primary Drinking Water Regulations (chlorine limit 4 mg/L)
- CDC — Home pool and hot tub water treatment and testing (pool chlorine minimum)
- City of Duluth — 2025 drinking water report (1.71 mg/L average)
- CDC — Water disinfection with chlorine and chloramine (why cities add chlorine)
- US EPA WaterSense — Showerheads (spray force vs water use)
- US EPA — Find your local water quality report
- Chlorine in your city — each city’s level comes from that city’s own yearly water quality report, linked on the card (checked 27 Oct 2026)