Tabletop RO systems?

[Ray]

Originally Posted by AlexJordan

The tabletop RO system you mentioned with five stages should be able to remove impurities such as chlorine, sediment, and some heavy metals, but may not be as effective in removing dissolved solids like minerals and salts. The frequency of filter replacements will depend on your water quality and usage, but it's generally recommended to replace them every 6 to 12 months.

That is not entirely accurate.

Suspended solids, usually down to 5µ, will be removed by the sediment filter.

Chlorine and organic chemicals will be effectively removed by the carbon filter.

Dissolved solids are removed by the membrane, and it does not matter if it's part of a 3-, 4-, or 5-stage RO system. Certainly a deionization (DI) cartridge as a final pass-though will remove more, but that's overkill.

Residential RO membranes output and efficiencies are rated using a 100 ppm NaCl solution at 77°F and 65 psi at the membrane housing, with the results being between 93% and 99% rejection, depending upon the membrane application. NaCl is an easy dissolved solid to reject; most "hardness minerals" are less so.

Every type of filter has volume limits on its efficacy. Commonly-used sediment filters are typically in the 2000-3000 gallon range. Carbons tend to be double that, and membranes are usually good for about 12,000 gallons. You can buy devices that totalize the input flow so you can monitor that, but folks just find it simpler to keep a 6/12/24 month replacement schedule. (However, having used, assembled, sold, and resold systems and components for 35+ years, I can tell you that most folks are sloppy about that...)