: Which is the best water filter? : What is "best" is different for everybody - quality and effectiveness, cost-effectiveness, or easy operation? The "best" filter is what suits your needs. Some people want the best quality regardless of money and complicated installation. Some want average quality and reasonable price, but are most concerned with easy installation and maintenance/care. Some are only concerned with exterior presentation. A balance should be sought among quality, price, operation and repair when buying a filter.     : What are the commonly used filtering materials and methods? : Depending on the water quality problem, different cities can use the following methods to process and filter their water:- 1) reverse osmosis 2) distillation 3) ion-exchange resin 4) granular activated carbon 5) ionization/ electrodialysis 6) filtration by fibre 7) filtration by ceramic Different materials and methods have its own advantages depending on the needs of the user.     : How many categories of filters are there according to the installation point? : A: There are basically three categories:- 1) On-tap type -- Directly installed on the sink tap. Small in size. Filter operates with the turn of a knob. This requires frequent change of cartridge with only limited effectiveness, but installation is easy! 2) Countertop type -- Water flows through plastic pipe connected to tap, then to filter and comes out. The filter is bigger and cartridge is more durable and effective. Installation is still simple and therefore quite popular. 3) In-line type -- connected within water pipes and in line can be classified into 3 kinds: -- a) undersink -- b) whole house centralized system -- c) ice maker unit/appliance cartridge Installation have to be done by professional plumber and would need pipe parts. Generally speaking this kind of filter has the best effect, saves space and is more visually sound.     : Is it necessary to change cartridge in filters regularly? : Yes. Impurities, silt and sediment in particular, must be cleaned out. It is important to change cartridges regularly. There are some cheap cartridges that are not bacteria resistant thus becoming a bacteria breeding ground. Drinking water filter cartridges should be bacteriostatic to ensure safe use. The frequency in changing cartridges varies according to the features of each model. Those kinds that are not bacteria resistant must be changed at least once every year.     : Apart from its filtering properties, what should we pay attention to when selecting a filter? : Other factors to consider when selecting a filter include flow rate, installation, complication in changing cartridges, price, and maintenance. If water passes through too fast, the cartridge does not have enough time to absorb impurities in the water, and its filtering capacity will be reduced. The water pressure in the pipes can also affect filters. Some filters cost relatively cheaper but cartridges are expensive and vice versa. Customers are advised to choose according to their needs.