If you've noticed that a filter cartridge or full system boasts an NSF 42 certification, you're probably wondering about the significance of this. When a system is certified for NSF 42, it means it has been third-party tested by an accredited body and deemed capable of eliminating or reducing chlorine or chloramines.
Note that some systems can reduce or remove both chlorine and chloramine, while some can only remove one or the other. Check to see exactly what a system is certified for - it may only be certified for filtering chlorine, and if your city water contains added chloramines, that's no use to you.