Filter size: 5 microns

Replacement cartridge:
Small - ~RM30 each
Big - ~RM600 each
*both can wait shopee / lazada voucher to maximize discounts

Small unit first, then big unit. Small filter can help reduce initial contents in water, reduce load in your bigger filter. Both filter replacement cartridge easy to DIY replace, can replace whenever water flow starts to be too slow for your liking. Small unit replace every 6 months or so. Big unit can replace every 2 years if your smaller unit is replaced properly.

Then if you want to install undersink, then can go with

3M undersink

Filter size: 1 microns
replacement cartridge: ~RM260
replace every: 1 year or 1.5 depending on your usage

total cost per year replacement estimate: (RM30 x 2) + (RM260) = RM320 / RM14 per month
total cost per 2 years replacement estimate: (RM30 x 4) + (RM260 x2) + RM600 = RM1240 / RM52 per month

Factors to consider:
- municipal water pressure (adding extra filters will lower water pressure)
- municipal water quality (within city should be cleaner, within developed states should be cleaner, hence prolonging your filter life and reduce replacement needs).
- water consumption needs (use more water = shorter filter life)

Not a seller / reseller for water filters, not water expert also, just sharing my basic setup for standard water quality

So far after I installed 3m, water quality improved significantly, clearly observable, done own testing (I am very intrigued by water related topics, hence I went to study and completed online degree for water management for my own curiosity). Besides that I still do boil water for consumption, my fridge also alot of space so use glass bottle to store purified or boiled water

On top of that no subscription fee for me, no need to arrange time for the filter fellas to come to only just "wash" the filters, used to have coway, but realized its RO filter, gave to my elders

Easy to replace filters, no significant change to my water pressure (landed) and installation hassle also one off, would recommend

edit: removed the extra spacing between lines