Looking at this cabon/kdf inline water filter for kitchen tap...
http://www.mountainfresh.co.nz/qcv1-kdf-kit---quick-change-kit.html
Regarding the KDF, figures show the copper/zinc are 10~20 time lower than FDA limit, I'd still get paranoid.
KDF seems popular for shower head in the states, I can't seem to find much info regarding safety of KDF filter for drinking water, i.e. the copper level before and after a KDF filter, compare to it's benefit on lead and mercury etc, test between GAC and GAC+KDF.
I might get the GAC only version - knowing GAC+KDF would in theory filter out more heavy metals and prolong filter life - albeit both are recommended to replace every 12 months, and that KDF would unavoidably add copper in.
Any thoughts or recommendations? Thanks.

