Chlorine injection for sulfur water

Best for

Wells with hydrogen sulfide above what air-injection or greensand filters handle, or with sulfur or iron bacteria that return after shock chlorination.

Wrong fit

Low or moderate levels that an air-injection filter can handle, and any home where only the hot water smells.

Tradeoff

It handles high levels and kills bacteria while it runs, but you refill chlorine, maintain a pump and filters, and replace carbon.

When chlorine injection is the right tool

Penn State Extension calls oxidation the most common treatment for hydrogen sulfide, and chlorine the usual oxidizer. It says chlorination can remove any level of H2S but is most often used when the concentration is above 6.0 mg/L (ppm). UGA Extension gives a working range of 6 to 75 ppm. Connecticut’s health department, Virginia Cooperative Extension and the Vermont Department of Health also point to injected oxidants at about 6 mg/L and above.

It’s the right tool when:

• Your H2S is above what an air-injection or greensand filter is rated for. SpringWell’s air-injection unit, for example, is published at 8 ppm.
• The smell comes from sulfur or iron bacteria and returns soon after each shock chlorination.
• You have high H2S plus iron or manganese that would overload a single oxidizing filter.

Alberta Agriculture leans toward chlorine even earlier. Its fact sheet says a manganese greensand filter typically handles less than 2 mg/L, has to be regenerated more often for H2S than for the same amount of iron, and can shed manganese that causes black stains, and concludes that a chlorine feed system is usually the better choice. US extension sources give greensand a higher ceiling, so treat this as one view rather than the rule.

It’s not the right tool when only the hot water smells (that’s the water heater), or when your level is low enough for a simpler chemical-free system. See the treatment-by-level table.

How the system works

A chlorine injection system has four parts in a row:

1. Chemical feed pump. Penn State says a small pump feeds chlorine solution, usually sodium hypochlorite, into the water line. It’s wired to run when the well pump runs, or paced by a flow sensor.
2. Contact (retention) tank or pipe coil. The chlorine needs time to react. Chlorine converts H2S to insoluble sulfur, a yellow solid, according to Penn State.
3. Sediment or backwashing filter. Catches the sulfur particles and any oxidized iron. UGA mentions a fine-retention sediment filter for yellow sulfur particles, and Connecticut a sand or aggregate filter that is backwashed regularly.
4. Activated carbon filter. Removes leftover chlorine and traces of H2S. Penn State says this may be necessary; UGA and Vermont note carbon gives chlorine-free water.

Dose and contact time

The sources broadly agree on the dose and mostly agree on contact time.

So for well water with 5 mg/L of H2S, the UGA ratio means roughly 11 mg/L of chlorine just to react with the sulfur, before any residual. Iron, manganese and organic matter use chlorine too. In practice the installer sets the pump so a small free chlorine residual remains after the contact tank, then lets the carbon remove it. UGA notes free chlorine above about 2 ppm can cause taste problems.

The shorter Alberta figure and the 20-minute figure from the US extension services aren’t really in conflict: Alberta also asks for 20 minutes when iron is present, which is common in sulfur wells. Use 20 minutes unless a water treatment professional who has seen your test results says otherwise.

Sizing the contact tank

Contact time depends on your peak flow rate. The math is simple: gallons of tank = minutes of contact x gallons per minute.

That’s a lot of tank for a small house, which is why installers sometimes use coils of plastic pipe, as Penn State mentions, or tanks designed to keep water from short-circuiting straight through. If space is tight, ask what contact time the installer’s design actually gives at your peak flow.

After the contact tank

Two things need removing: the sulfur particles and the leftover chlorine.

• Sulfur particles. Penn State says filtering them out is often unnecessary, but if yellow particles show up in fixtures or laundry, a backwashing sand filter or a fine sediment cartridge handles them.
• Chlorine residual. A whole-house carbon filter, or a carbon filter only on the kitchen tap if you don’t mind a slight chlorine smell elsewhere. UGA notes a carbon filter can supply chlorine-free water for drinking and cooking.

Alberta Agriculture adds several install details worth checking on any quote:

• Iron goes first. Its most common layout is a chlorine feeder, a retention tank and a full-size carbon filter, which it says suits water with H2S and no significant iron. With significant iron, it recommends a large sediment filter ahead of the carbon so iron doesn’t shorten the carbon’s life.
• Backwash flow. The well has to supply enough water to backwash the filters. Alberta says a typical 10-inch filter needs at least 5 gallons per minute to backwash properly.
• Drain valve. A valve at the bottom of the retention tank lets you drain settled sediment.
• Test valves. Chlorine test valves just after the pressure tank and just before the carbon filter let you check the chlorine level and adjust the feeder.
• Wiring. The chlorinator is wired to the pressure switch, so it runs whenever the well pump does.

Maintenance and running costs

Penn State says chlorination systems need significant maintenance. Expect to:

• Refill the chlorine solution tank on a schedule that depends on your water use and dose.
• Check the chlorine residual with test strips or a kit.
• Backwash or change the sediment filter.
• Replace the carbon when chlorine or sulfur starts getting through.
• Keep the injection pump clean and its check valve working.

Downsides

• Chemical handling. You store and mix chlorine.
• Taste. Without a carbon filter, treated water tastes of chlorine.
• Not always recommended for iron bacteria. The Minnesota Department of Health says it doesn’t usually recommend continuous chlorine injection for iron bacteria, because it can mask other bacterial contamination and cause corrosion. Its usual approach is physical cleaning and shock-treating the well. That’s a reason to try shock chlorination first when bacteria are the cause.
• Space. The contact tank, filters and solution tank take floor space.

Chlorine vs other oxidizers

Potassium permanganate works the same way, with at least 15 minutes of contact and a greensand filter, per Penn State, but it’s an irritant and poison to handle. Hydrogen peroxide leaves no chlorine taste, but extension guidance on household peroxide systems is limited. See hydrogen peroxide for sulfur water. Alberta Agriculture lists peroxide, permanganate and ozone as the alternatives to chlorine, and notes that filtration is still needed after any of them. If your levels allow it, an air-injection filter avoids chemicals altogether.

SpringWell’s chemical injection system

SpringWell sells a chlorine injection system. Its product page says chlorine injection “kills iron bacteria while oxidizing iron, sulfur and manganese”, lists automatic dosing via a flow sensor, a 35-gallon tank (18 by 33 inches), a 1-inch connection, 10 to 150 psi, and 1 to 7 bathrooms. The page lists “up to 12+ GPM” in one place and “30 GPM service” in the spec table.

The page doesn’t publish a hydrogen sulfide limit, and it doesn’t say whether the 35-gallon tank is the solution tank or a contact tank, or whether a carbon filter is included. Before buying, ask SpringWell what contact time the system gives at your peak flow, whether you need a separate contact tank, and what filter they recommend after it.