Tried a shower filter and felt no difference? There's a likely culprit: chloramine.
What it is
Many cities have switched from chlorine to chloramine — a chlorine-ammonia compound — to disinfect water. It's more stable than chlorine, which is great for pipes and rough on hair: it doesn't off-gas in a hot shower, and basic carbon filters barely touch it.
How to know what's in your water
Search your city's name plus "water quality report" — every U.S. utility publishes one. Look for "chloramine" or "monochloramine" under disinfectants.
What filters it
Vitamin C (ascorbic acid) neutralizes chloramine on contact, which is why a dedicated Vitamin C stage matters in a shower filter. The Lumen Filter Showerhead pairs a Vitamin C stage with KDF-55 and calcium sulfite, so both chlorine and chloramine are covered — including in hot water, where chlorine compounds do the most damage to curls.