hey. yes you do not need activated carbon for your external water filter. Pentair (external water filter brand that im using) uses three types of silica sand, zeolite and garnet. Water will be free from soluble heavy metals, ammonium and other suspended solids. still contains chlorine.

as for internal water filter im using Espring that has NSF certifications of 42, 53 and 55 (kills 99.99% of bacteria and viruses). maintenance is low, rm0.10/litre only.

actually a good activated carbon removes quite a huge number of harmful contaminants. we just dont want it on our POE coz it eliminates chlorine as well. say for Espring (internal water filter), its activated carbon can remove 140 health-effect contaminants (all are listed and documented).

for rm4800, i suggest u go for pentair and espring. price includes installation also. pm me if u'd like to know more.