Treating well water for the whole house, in order

Test before you buy anything

EPA says private wells are not regulated under the Safe Drinking Water Act, nor by most states, so the owner is the only one testing. Its advice is to test every year for total coliform bacteria, nitrates, total dissolved solids and pH, and to use a lab certified for drinking water. The well testing guide covers when to test again.

Test before you shop, too. Penn State Extension says to get results from a state-certified lab and review them with an unbiased expert before buying equipment, and warns that some sellers use colorful home tests to pressure buyers. Nebraska Extension says the same: test first, whatever system you are considering.

What the result points to

What the test or your eyes show	The usual whole-house treatment	What certifies it
Sand, silt or cloudiness	Sediment filter	NSF/ANSI 42, "Nominal Particulate Reduction"
Orange or brown stains, iron above 0.3 ppm	Oxidizing iron filter, or a softener for low dissolved iron	WQA's "Iron" claim under NSF/ANSI 42, seen on one maker's systems
Black stains, manganese	Oxidizing filter such as manganese greensand	No product listed with a manganese claim on October 4, 2026
Rotten-egg smell	Carbon, catalytic carbon or an oxidizing filter, depending on the level	WQA's "Hydrogen Sulfide" claim under NSF/ANSI 42, seen on one maker's systems
Scale, spots, hard water	Water softener	NSF/ANSI 44, "Hardness Reduction"
Coliform bacteria	UV or continuous chlorination	NSF/ANSI 55, "Disinfection Performance, Class A"
Radon	Aeration or granular activated carbon	See EPA's radon guidance, below
Arsenic or nitrate	Usually reverse osmosis at the kitchen tap	NSF/ANSI 58

Iron and hydrogen sulfide certifications are rare. NSF lists iron and manganese as possible NSF/ANSI 42 claims, but on October 4, 2026, its listing search showed no product with either, and WQA showed its iron and hydrogen sulfide claims only on systems from one maker. Every other iron and sulfur filter is sold without a certification for it, so the whole-house register labels each one.

The order, and why

No single agency publishes the whole sequence on one page, but every link in it comes from extension and health department guidance.

1. Sediment first. UGA Extension advises a whole-house sediment filter ahead of a carbon filter, and Nebraska Extension says sediment filters go ahead of carbon and reverse osmosis. Minnesota's health department says one ahead of a softener can help too.
2. Iron, manganese and sulfur next. Nebraska Extension says iron above 5 ppm or hydrogen sulfide reduces a softener's effectiveness, and that pre-softening equipment should go in if needed. Minnesota's health department says iron or manganese exposed to air or chlorine can clog softener resin.
3. Softener, if you want one. Minnesota's health department says a softener may be worth it above 7 grains per gallon, and calls softening a personal choice rather than a requirement. Softener or salt-free conditioner covers the trade-offs, including sodium.
4. UV last. Connecticut's health department says UV is often the last device in the treatment train, after filtration and softening. Virginia Cooperative Extension says cloudy water and sediment limit UV, which is why it goes at the end.

Iron and sulfur: the level decides the equipment

Penn State Extension's ranges for iron and manganese:

• A softener generally only when pH is above 6.7, hardness is 3 to 20 grains per gallon, and dissolved iron is under 5 mg/L. Other sources set the softener limit lower: the University of Minnesota says about 3 mg/L.
• Manganese greensand for combined iron and manganese of about 3 to 10 mg/L, regenerated with potassium permanganate and backwashed.
• Oxidation then filtration, with chlorine, potassium permanganate or hydrogen peroxide, above about 10 mg/L.

Penn State's ranges for hydrogen sulfide, the rotten-egg smell:

• Plain activated carbon below about 1 mg/L.
• Catalytic carbon handles much higher levels than plain carbon, but needs at least 4 mg/L of dissolved oxygen and still needs backwashing.
• Oxidizing filters up to about 2 to 3 mg/L. Minnesota's health department puts the limit for oxidizing media such as greensand higher, at about 6 mg/L.
• Chlorination or permanganate feed above about 6 mg/L.

If only the hot water smells, the water heater may be the source rather than the well. Penn State says the heater's magnesium rod can produce the gas, and an aluminum rod should end the smell while keeping its corrosion protection. Minnesota's health department adds that the gas can be harmful in the air at high levels, and should be vented from well pits and basements.

Most iron and sulfur filters backwash to a drain, so plan for a drain line at the install location.

UV: Class A, clear water, and no leftover disinfectant

UV shines light on water as it flows past a lamp, inactivating bacteria, viruses and cysts. It adds nothing to the water and removes no chemicals.

Buy Class A. NSF says NSF/ANSI 55 Class A systems inactivate bacteria, viruses and cysts in contaminated water, while Class B only reduces harmless bacteria in water that is already disinfected. WQA says Class A delivers at least 40 mJ/cm² and must include an alarm and a UV sensor. Class B delivers 16 mJ/cm².

Feed it clear water. Penn State Extension says water entering a UV unit must be completely clear, often with a sediment filter ahead of it, and hard water can coat the lamp sleeve with scale. WQA says cloudiness, metals and some other chemicals absorb or block the light.

Know its limits. Penn State does not recommend UV when total coliform tops 1,000 colonies per 100 mL or fecal coliform tops 100, and Virginia Cooperative Extension gives the same numbers. UV also leaves no disinfectant behind, so germs that get into the plumbing after the unit are not treated. Continuous chlorination, by contrast, aims to leave about 0.3 to 0.5 mg/L of chlorine in the water, according to Penn State.

Radon is whole-house or nothing

EPA says whole-house treatment can remove radon before it reaches the plumbing, usually with aeration or granular activated carbon, and that a filter at one tap does not reduce the risk from breathing radon released by all the water in the house. EPA's table gives aeration 95 to 99 percent removal and carbon 85 to 95 percent, and says carbon suits moderate levels of around 5,000 pCi/L or less. EPA also says radon entering a home through water is, in most cases, a small risk compared with radon from the soil.

What stays at the kitchen tap

Some well problems are better solved at one faucet. Penn State Extension says reverse osmosis for arsenic and nitrate is usually an under-sink unit. Minnesota's health department says not to give water with nitrate to babies under six months, even after home treatment, in case the treatment fails. EPA's legal limits for public water, 10 ppm for nitrate and 10 ppb for arsenic, are a sensible line for a well. See nitrate and arsenic.

After it's installed

Nebraska Extension says to retest after installing treatment. For UV, Connecticut's health department says to test both raw and treated water, to test treated water for coliform monthly for at least the first six months, and to test every year after that.

What it costs

Penn State Extension says most whole-house units, including softeners, carbon and oxidizing filters, cost $500 to $1,500, and UV systems run from about $400 for a basic unit to more than $1,000 with a light sensor and automatic shutoff. It does not say whether that includes installation. At those ranges, an iron filter, a softener and UV alone come to roughly $1,400 to $4,000 or more before a plumber touches them. The five-year cost calculator takes your plumber's quote and adds it to the media and parts.