Fitting an RO system takes half a day. What deserves more thought is what comes before: does my water justify reverse osmosis, can my sink cabinet take it, and will I genuinely keep up the maintenance. This section handles those three separately, because a system bought for the wrong reasons ends up unplugged within a year — the worst outcome for your wallet and for your water alike.
The order to take them in
1. The need first. Reverse osmosis is the most complete answer, and also the heaviest. If your only complaint about the tap is a chlorine taste, a $35 carbon filter will do; reverse osmosis vs pitcher filter draws the line precisely. RO becomes the right call for lead, PFAS, nitrate and arsenic — or for water you refuse to drink to the point of buying cases of bottles.
2. Feasibility next. An under-sink system needs room for the housings and a 3-gallon tank, a tee on the cold line, a drain connection for the reject, and a hole for the dedicated faucet. In a rental, that hole can be the sticking point: there are adapters that replace the aerator on the existing faucet — less elegant, but reversible.
3. Maintenance last, and above all. This is what decides everything. Prefilters every 6 to 12 months, membrane every 2 to 3 years, $50 to $80 a year. If you know in advance that you will not do it, do not buy reverse osmosis: a simpler filter, covered in the filtration section, will age better in your hands.
The mistakes people regret
Buying RO for hard water. Reverse osmosis only treats the water at its own dedicated faucet; your water heater goes on scaling up happily. Against scale throughout the house you want a softener, and checking your hardness is the starting point. Ignoring hard water upstream: a membrane fed 18 gpg water wears out roughly twice as fast, which changes the consumables arithmetic. Losing track of cartridge dates: a saturated filter stops filtering, and a neglected RO system is worse than no RO system at all. A reminder in your phone on installation day settles it permanently.
