Whole-House and Under-Sink Water Filtration: Types, Installation, and Maintenance

Start with a Water Test

Don't buy filtration equipment until you know what you're filtering. Municipal water customers can request a free Consumer Confidence Report (CCR) from their utility, which lists contaminant levels. This tells you what's in the water when it leaves the treatment plant — not necessarily what comes out of your tap after traveling through aging pipes.

For a more complete picture, or if you're on well water, get a laboratory test. Mail-in kits from certified labs cost $100 to $300 depending on the panel. Test for the basics (pH, hardness, iron, manganese, TDS, coliform bacteria, nitrates) and add specific tests if you have concerns (lead, arsenic, PFAS, VOCs). The lab results will tell you what's elevated and by how much, which directly determines what filtration technology you need.

Whole-House Sediment Filters

A whole-house sediment filter installs on the main water line where it enters the house, upstream of the water heater and all fixtures. It catches particulate matter — sand, rust, silt, and pipe scale. This is the most basic and most universally useful form of filtration.

Spin-down filters have a reusable mesh screen (typically 100 to 25 microns) that you flush periodically by opening a valve at the bottom. Cartridge filters use replaceable pleated or wound cartridges (typically 20, 10, 5, or 1 micron) in a filter housing. Cartridge filters catch finer particles but require filter changes every 3 to 6 months depending on your water quality.

Installation requires cutting into the main water line and adding the filter housing with shutoff valves on both sides. If your main line is copper, you'll need a pipe cutter, fittings, and either solder (torch, flux, solder) or push-fit connectors (SharkBite or similar). PEX or CPVC lines are easier to cut into. A bypass loop with a valve lets you service the filter without shutting off water to the whole house.

Under-Sink Reverse Osmosis

Reverse osmosis (RO) is the most thorough point-of-use filtration available. It forces water through a semipermeable membrane that removes dissolved solids, heavy metals, fluoride, PFAS, and most contaminants down to the molecular level. A typical under-sink RO system has 3 to 5 stages: sediment pre-filter, carbon pre-filter, RO membrane, and a carbon post-filter for taste.

RO systems waste water — for every gallon of filtered water, 2 to 4 gallons go down the drain. Newer systems with permeate pumps or recirculation reduce this ratio. The waste water carries the rejected contaminants and can be directed to a garden or collection barrel if your local code allows it.

Installation fits under a standard kitchen sink. You'll need to tap into the cold water supply line (a self-piercing saddle valve or a tee fitting), install the dedicated faucet through the sink or countertop (requires a hole if one doesn't exist), and connect the drain line to the sink's drain pipe above the trap. Most systems come with push-fit tubing connections that don't require tools beyond a drill for the faucet hole.

Carbon Filtration

Activated carbon filters are the workhorse of taste and odor improvement. They adsorb chlorine, chloramine (the treatment chemical that makes water taste like a pool), volatile organic compounds, and some pesticides. They don't remove dissolved minerals, heavy metals, or bacteria.

Granular activated carbon (GAC) is cheaper and offers less contact time. Carbon block filters are denser and more effective per volume but restrict flow more. For a whole-house application, oversized GAC housings work well. For under-sink point-of-use, carbon block is the better choice.

Filter replacement is the ongoing cost. Most carbon filters last 3 to 12 months depending on the filter size and your water usage. Track the install date and replace on schedule — an exhausted carbon filter can release accumulated contaminants back into the water.

UV Disinfection

Ultraviolet disinfection kills bacteria, viruses, and protozoa by damaging their DNA. It's essential for well water systems that test positive for coliform bacteria and useful as a secondary barrier for anyone concerned about biological contamination.

A UV system installs inline on the main water line, typically after sediment and carbon filtration (the water must be clear for UV to work — turbidity blocks the light). The UV lamp operates continuously and needs replacement annually. The quartz sleeve around the lamp needs periodic cleaning to maintain light transmission.

UV treats what passes through it at that moment — it provides no residual disinfection. If bacteria enter the system downstream of the UV unit (from a leaky fitting, for example), the UV won't protect against it. Place the UV unit as the last stage before distribution.

Maintenance Schedule

Whole-house sediment filter: replace cartridge every 3 to 6 months, or sooner if water flow drops noticeably. Write the install date on the cartridge with a permanent marker.

Carbon filters: replace every 6 to 12 months. Whole-house carbon filters that treat high-volume usage may need more frequent changes. Under-sink carbon blocks typically last 6 months at standard household usage.

RO membrane: replace every 2 to 3 years. Pre-filters and post-filters on the RO system need replacement every 6 to 12 months — these protect the membrane, so don't skip them.

UV lamp: replace annually regardless of whether it appears to be working. UV output degrades over time and a dim lamp may not deliver sufficient dose for disinfection. The quartz sleeve should be cleaned every 6 months and replaced if scratched or clouded.

Frequently Asked Questions