Air-injection sulfur filters

Best for

Wells with hydrogen sulfide in the low-to-moderate range, often with some iron or manganese, pH within the unit's range, and no bacteria problem.

Wrong fit

Wells above the unit's published limits, wells with coliform bacteria or a heavy sulfur or iron bacteria problem, and any home where only the hot water smells.

Tradeoff

No chemicals to buy or refill, but it needs a drain for nightly backwash, a power outlet, and enough pump capacity, and it won't fix bacteria.

How an air-injection filter works

An air-injection oxidizing filter (often sold as an “AIO” system) does three jobs in one tank:

1. Oxidation. The top of the tank holds a pocket of air. As water passes through it, oxygen converts dissolved hydrogen sulfide, iron and manganese into solid particles.
2. Filtration. A bed of filter media below the air pocket traps those particles.
3. Backwash. On a schedule, the control valve reverses flow, flushes the trapped particles to a drain, and draws in fresh air to rebuild the pocket.

SpringWell describes its single-tank unit this way: water passes through “an oxygen-rich pocket at the top of the tank”, a “greensand fusion” media bed catches the oxidized particles, and a backwash runs each night. Nothing is added to the water, so there’s no chemical tank to refill.

Air injection vs simple aeration

Extension sources usually describe plain aeration, where air strips the gas out of the water. Penn State Extension says aeration is normally not used above about 2 mg/L (ppm) of hydrogen sulfide, and Connecticut’s health department and UGA Extension also put it below 2.0 mg/L. Penn State adds that aeration can form sulfur particles that need filtering.

An air-injection oxidizing filter goes further, because the media bed both filters and helps oxidize what the air didn’t finish. That’s why manufacturers rate these units higher than plain aeration. The published figure for SpringWell’s unit is 8 ppm H2S.

This is a place where sources differ. The extension limits for aeration (about 2 mg/L) and for oxidizing filters (2 to 3 mg/L per Penn State, about 6 mg/L per Minnesota and Virginia, up to 10 ppm per UGA) were written about related but not identical equipment. A manufacturer’s 8 ppm rating is that company’s own specification, not an independent test. The most cautious source is an older Alberta Agriculture fact sheet, which says some chemical-free aeration-type iron filters have removed small amounts of H2S, but only where the water carries much more iron than H2S. If your level is near the top of the range, ask the seller how the rating changes when iron and manganese are also present, and consider retesting, since Virginia Cooperative Extension notes H2S levels are often seasonal.

Published limits for one example unit

SpringWell’s spec page lists these figures for its Whole House Well Water Filter (WS1 and WS4):

The page lists the H2S, iron and manganese limits separately. It doesn’t say whether all three can be at their maximums at once. If your water is high in more than one, ask before buying. The full write-up is in our SpringWell sulfur filter review.

Who it fits, and who it doesn’t

SpringWell’s spec page says plainly not to use its unit where water is microbiologically unsafe, and asks for a complete water test before purchase. Penn State recommends disinfecting aerated water.

Install requirements

Before you buy, check that your house can take one:

• A drain for the backwash line, such as a floor drain or laundry standpipe, within reach of the tank. The backwash carries the trapped sulfur and iron out of the house, so ask the seller how much water each backwash uses, especially if you’re on a septic system.
• Power. The control valve runs on household power. SpringWell’s kit includes a power supply.
• Space and height. SpringWell’s tanks are 54 inches tall, 64 inches with the valve head, and 10 or 13 inches wide.
• Water pressure within the unit’s range (25 to 80 psi for SpringWell’s).
• Pump capacity. Backwash needs a certain flow rate. Ask the seller what flow the backwash requires and check it against your well pump and pressure tank.
• Placement. After the pressure tank and any sediment filter, and before a softener, a UV unit or a whole-house carbon filter.
• Licensing. Some states require a licensed plumber or water conditioning contractor. Minnesota advises checking an installer’s license, and Wisconsin requires treatment devices to be installed by licensed plumbers, with an exception for some owner-occupants of single-family homes.

Maintenance

Air-injection filters are low-maintenance compared with chemical systems, but not no-maintenance.

• Check the backwash. Make sure it runs on schedule and the drain line isn’t kinked or frozen.
• Watch for a returning smell. It’s often the first sign the air pocket isn’t recharging or the media is fouled.
• Media replacement. The media wears out eventually. SpringWell claims more than 10 years of media life for its unit; that is a manufacturer claim, and actual life depends on your water.
• Pre-filter. If you have a sediment filter ahead of it, change the cartridge on schedule.

When the smell comes back

Work through these in order:

1. Hot or cold? If only the hot water smells now, the water heater is making its own gas. See hot water smells like rotten eggs.
2. Bacteria. Sulfur bacteria can live in the well, pressure tank and pipes beyond the filter. A smell that is strong when a tap first opens and then fades points this way. Minnesota recommends shock chlorinating the well and plumbing. See shock chlorination.
3. Bacterial slime. Minnesota says sulfur bacteria produce a slime that can clog wells and plumbing and help iron bacteria grow. That slime can foul filter media too.
4. Level changed. Retest. If H2S is now above the unit’s limit, the fix is a stronger method, not more backwashing.
5. Air pocket. Call the maker’s support line to check the air draw and backwash settings.

Questions to ask before buying

Bring your lab results and ask the seller, in writing if you can:

• Combined limits. Can the unit handle my hydrogen sulfide, iron and manganese levels all at once, at my pH? Published limits are usually listed one contaminant at a time.
• Basis for the rating. Is the H2S figure from independent testing or certification, or the maker’s own specification?
• Backwash water and flow. How many gallons does each backwash use, what flow rate does it need, and can my well pump and pressure tank supply it? This matters more on a low-yield well or a septic system.
• Schedule. How often does it backwash, and can the schedule be changed if the smell returns between cycles?
• Media life. When will the media need replacing, and roughly what does that involve?
• If it doesn’t work. What does the guarantee cover once the unit is installed, as opposed to returned unused? Our SpringWell review walks through one company’s terms.

A seller who answers these from your actual test numbers, rather than a general rating, is a better sign than any single spec.

Air injection vs chlorine injection

If your numbers fit inside an air-injection unit’s limits and bacteria aren’t a problem, it’s usually the simpler choice. SpringWell’s well water filter is one unit published at those limits. If they don’t fit, the treatment-by-level table shows the next step up.