WHAT’S IN YOUR WATER SEDIMENT · CARBON · MEMBRANE

What’s actually in your water — and what to do about it.

We’re chemists who live on a well in New England. A firefighting-foam plume reached our water, a contractor’s shortcut let it happen again, and a whole-house filtration system we bought online to fix it didn’t perform as claimed — three failures with the same root cause: we didn’t have the right information before we spent the money. This site is the resource we wish we’d had: built by chemists, written for homeowners, organized so you understand your water before you spend a dollar on it. It’s educational first. When we do point you toward products — sold directly or through affiliate links — it’s based on quality and performance, not who pays us most.

The Filtration Short Course

Water problems fall into a small number of categories, and each one has a mechanism built for it. Learn the mechanisms first, and every filter, contaminant, and product on this site will make sense on sight — instead of feeling like a list to memorize.

Sediment Filtration

Water is forced through a tortuous path inside the filter material, and particles get trapped along the way as it winds through — the filter essentially strains them out as it goes. A filter’s micron rating tells you the smallest particle size it’s built to catch: a coarse filter catches sand and silt, a finer one reaches down to bacteria and some cysts. This is the most intuitive mechanism, but it only works on things that are actually particles. Anything dissolved passes straight through, no matter how fine the rating.

Sediment and carbon are usually the first line of defense in a multi-stage system — sediment protects everything downstream from clogging on particles, and carbon protects chlorine-sensitive stages like RO membranes. That’s a sequencing fact, not a recommendation: which stages you actually need still depends on what’s in your water.

Nominal vs. absolute is worth knowing before you shop: a nominal rating is a rough average (some particles above that size get through); an absolute rating is a guarantee (that size and up gets caught, tested to prove it). Nominal vs. absolute is a marketing label, not a quality grade on its own — check which one a product actually claims.

Common depth-filter types:

  • Pleated — folded material gives more surface area, so it handles higher flow and lasts longer. Common for whole-house use.
  • Melt-blown — layered fine fibers, denser toward the surface. Reaches finer particle sizes, common for drinking-water applications.
  • String-wound — the simplest and least expensive construction. Coarser and shorter-lived than the other two, but a reasonable low-cost first stage.
Good forSediment, silt, rust, cysts, some bacteria.
Not forAnything dissolved — salts, metals, nitrate, PFAS.

Carbon Filtration (Adsorption)

Carbon filtration is the gold standard for chemical and taste/odor removal. Contaminants stick to the surface of activated carbon as water passes through it — the material is riddled with microscopic pores, giving it enormous surface area to grab onto chlorine, many chemicals, and things that affect taste and odor. This is adsorption: contaminants held on a surface, not caught in a mesh.

Carbon exhausts silently. Once its surface fills up, it stops working — there’s no warning built into the filter itself, which is why cartridge replacement schedules matter more for carbon than for sediment.

One distinction worth knowing: standard carbon removes chlorine well but does very little for chloramine (a more common disinfectant now in many municipal systems). Chloramine needs catalytic carbon, a version of activated carbon treated to react with chloramine rather than simply adsorb it. If your water is chloraminated, plain carbon isn’t the right tool.
Good forChlorine, chloramine (catalytic carbon only), many chemicals and VOCs, taste and odor.
Not forMost metals, nitrate, hardness, PFAS reliably at low cost — and it has a capacity ceiling rather than a warning light.

Ion Exchange

Water passes over a resin bed that swaps one dissolved ion for another. A softener swaps calcium and magnesium (hardness) for sodium. A nitrate-selective resin swaps nitrate for chloride. It’s precise — but only for the ion it’s built to grab, and a resin can release its stored load if it’s allowed to exhaust rather than being regenerated on schedule.

Good forHardness, nitrate, some forms of arsenic, tannins.
Not forAnything outside what the specific resin is selective for — a softener will not touch nitrate, and a nitrate resin will not soften your water.

Oxidation & Aeration

A dissolved substance reacts with an oxidizer — often just air — and turns into a solid particle, which a sediment filter downstream then catches. This is always a two-step process: react it, then catch it. Oxidation alone, with nothing behind it, does not remove anything from the water.

Good forDissolved iron, manganese, hydrogen sulfide.
Not forAnything that isn’t chemically oxidizable — and it needs a filtration stage after it to actually finish the job.

Reverse Osmosis

Reverse osmosis is the gold standard for household water treatment. Water is pushed under pressure through a dense membrane fine enough to block most dissolved and suspended contaminants — salts, metals, most chemicals, some microorganisms. It’s the broadest-spectrum single method here. The tradeoff: it also removes the beneficial minerals along with what you don’t want, producing demineralized water some people choose to remineralize afterward.

Pre- and post-treatment matter. RO membranes need protecting: sediment ahead of it stops particles from clogging the membrane, and carbon ahead of it stops chlorine from degrading it. On hard water, softening beforehand extends membrane life. A polishing carbon stage afterward removes any remaining taste.

Most residential RO serves a single tap (typically the kitchen), with a small tank for on-demand flow. Whole-house RO exists and is growing more common, but it’s a bigger, more complex installation — more pre-treatment, more capacity, more plumbing.

Good forThe widest range of contaminants of any single method — dissolved or particulate, at the speed a household actually uses water.
Not forA casual whole-house retrofit — it produces some wastewater as part of the process, and treating your whole house this way is a significantly bigger project than an under-sink system.

Distillation

Water is boiled to vapor and condensed back to liquid, leaving dissolved solids behind. By raw chemistry, distillation reaches nearly the same contaminant list as reverse osmosis — lead, arsenic, nitrate, fluoride, salts, hardness, PFAS — through a completely different mechanism. On paper, that makes them peers, not a hierarchy.

In practice, they’re not interchangeable for a household. Distillation is slow — hours per batch, a few quarts at a time — and boiling water at any real volume takes meaningful electricity. That gap is wide enough that distillation isn’t a realistic whole-house or even whole-kitchen supply; it’s why it’s excluded from system recommendations in the configurator rather than offered as a slower alternative to RO.

The counterintuitive catch: some volatile chemicals (VOCs) boil at similar temperatures to water and travel with the vapor, meaning distillation alone doesn’t reliably remove them — pairing distillation with a carbon stage closes that gap.
Good forSmall-volume, mineral-free water for specific uses — CPAP humidifiers, steam irons, batteries — and off-grid situations where RO’s continuous wet brine discharge is the harder problem to solve, not distillation’s slowness.
Not forEveryday household drinking or whole-house supply — RO wins decisively there on speed and energy alone.

UV Disinfection

Ultraviolet light disrupts the DNA of bacteria, viruses, and protozoa as water passes through a UV chamber, so they can’t reproduce. This inactivates microorganisms — it does not remove them physically, and it does nothing for anything that isn’t alive (chemicals, metals, sediment).

Three things UV needs to actually work:

  • Clear water. Turbidity or sediment can shield organisms from the light, so a sediment (and often carbon) pre-filter is standard ahead of a UV stage.
  • The right flow rate. UV units are rated for a specific flow; pushing more water through than rated reduces the dose each organism receives.
  • Continuous power. No power, no disinfection — worth a thought if you’re in an area with frequent outages.
Good forBacteria, viruses, protozoa — once the water reaching it is already clear.
Not forWater with meaningful sediment or turbidity on its own; anything non-biological.

Point of Entry (POE) vs. Point of Use (POU)

Once you know which mechanism handles your problem, the next question is where it needs to sit — the whole house, or one tap.

Point of Entry (whole-house). Installed on the main line where water enters the home, so everything downstream — bathing, cooking, laundry, every fixture — gets treated. Common install spots: near the water heater, in a garage, basement, mechanical room, or crawl space, with access to power and a drain where the stage needs one.

If your home was built after the 1970s, look for a softener loop — a three-valve bypass built into the plumbing specifically to make adding a whole-house filter or softener straightforward later.

POE systems typically use larger cartridge housings (commonly 4.5″ diameter) or tank-style media beds, since they need to handle the flow demands of an entire household.

Point of Use (at the tap). Installed at a single point — usually under the kitchen sink, though also countertop, refrigerator-line, or pitcher formats. Built for drinking and cooking water specifically, not for treating everything in the house.

POU cartridge systems typically use smaller housings (commonly 2.5″ diameter), suited to lower flow demands and easier self-service.

Choosing between them. Some contaminants genuinely require whole-house treatment — hardness will scale your whole plumbing system regardless of what comes out of the kitchen tap, and a pathogen risk shouldn’t be limited to one faucet if it’s present in the supply. Others are purely a drinking-water concern, where a single tap is the honest, lower-cost answer. Many households end up with both: a whole-house stage for a house-wide issue, and a tap-specific stage layered on top for drinking water quality.

Where to go next:

  • Not sure what’s actually in your water? → Take the quiz below
  • Know what’s actually in your water first → Test Your Water
  • Already know what you’re dealing with → Build Your System

Frequently Asked Questions

What’s the most effective single method?

Reverse osmosis is the gold standard for household water treatment — the broadest range of dissolved contaminants of any single method, at a speed a household can actually use. Distillation reaches a similar contaminant list by raw chemistry, but its real-world slowness and electricity use rule it out for everyday household supply — it’s reserved for small-volume needs and specific off-grid situations. Neither is a universal fix for everything — sediment and chlorine are typically better handled by dedicated stages ahead of either one.

Is there a filter that removes everything?

No single method removes every possible contaminant — that level of purity is reserved for lab and medical applications with continuous monitoring, and isn’t necessary or realistic for a home. The honest goal is matching a method to what’s actually in your water.

Should I test before I filter?

Yes. Buying a system before you know what’s actually in your water means guessing — see Test Your Water for how to get a real answer, city or well.

Do I need a whole-house system, or just something at the tap?

Depends on the contaminant, not preference — see the POE vs. POU section above. Some things need whole-house treatment; many concerns are drinking-water-only.

Is filtered water healthier than tap water?

It depends entirely on what’s in your specific tap water and what the filter is actually rated to remove — there’s no universal answer without knowing both sides of that equation.

A filtration company quoted you. Your neighbor has opinions. Your water report says something you can’t pronounce. Whatever brought you here — this is where you sort it out. Figure out what you need, and just as importantly, what you don’t.

Don’t know what you have? Start with the quiz.

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