For broad contaminant reduction with zero permanent plumbing, countertop reverse osmosis is usually the strongest renter option. For lower cost, a certified pitcher or faucet filter can work when its exact claims match the water problem.
Best overall category: countertop reverse osmosis
Countertop RO systems are attractive for apartments because they can provide broad dissolved-contaminant reduction without modifying building plumbing. Many simply plug in and use a refillable feed tank.
The tradeoffs are counter space, electricity, proprietary filters and a higher upfront cost than a pitcher.
Best budget category: certified pitcher filters
A pitcher is the easiest option to move between apartments. The critical issue is certification scope: one pitcher may only improve chlorine taste while another carries specific lead or PFAS claims.
Do not judge by TDS reduction alone. A low TDS reading does not identify which contaminants were removed.
Best on-demand category: faucet-mounted filtration
Faucet filters provide filtered water on demand and can often be removed without permanent plumbing changes. They are best when a compatible removable aerator is available.
Pull-out spray faucets and proprietary aerators can make installation impossible or awkward.
What renters should test before buying
The building can add plumbing-related contaminants after water leaves the utility. A Consumer Confidence Report is useful, but a tap-level test can be more relevant when lead, copper or old-building plumbing is the concern.
A mail-in laboratory service such as Tap Score is especially useful before spending several hundred dollars on a purifier.