Chemical injection systems for well water

Best for

Wells with iron, manganese or hydrogen sulfide above what air-injection or greensand filters handle, or with iron or sulfur bacteria that keep coming back.

Wrong fit

Homes with moderate levels inside an oxidizing filter's range, or with a single positive coliform test. Try the simpler fix first: a matched oxidizing filter, or shock chlorination and a retest.

Tradeoff

It is the most hands-on option: you mix and refill solution, maintain a pump and change carbon, and you may taste chlorine without a carbon filter.

What a chemical injection system does

A chemical injection system (also called a chlorinator or chemical feed system) adds a measured dose of oxidant to your water as it flows. The oxidant does two jobs:

• It converts dissolved iron, manganese and hydrogen sulfide into solid particles that a filter can catch.
• If enough of it stays in the water long enough, it kills bacteria, including the iron and sulfur bacteria that cause slime and odor.

Penn State Extension says chlorine, usually sodium hypochlorite, is the most common oxidant. Potassium permanganate and hydrogen peroxide are alternatives. Peroxide leaves no chlorine taste, while permanganate is an irritant and poison that needs careful storage.

How it works, step by step

1. Flow sensing. A flow switch or meter detects water moving and turns on the pump. SpringWell’s system uses a flow switch box that powers the pump only while water is flowing.
2. Injection. A small metering pump draws solution from a tank and pushes it into the water line through an injection fitting.
3. Contact time. The water then passes through a mixing tank or a coil of plastic pipe so the reaction can finish. Penn State recommends at least 20 minutes of contact for hydrogen sulfide with chlorine, and about 30 minutes when the goal is disinfection.
4. Filtration. A backwashing filter removes the iron, manganese and sulfur particles.
5. Polishing. A carbon filter removes leftover chlorine taste and odor.

Steps 3 to 5 matter as much as the pump. SpringWell’s product page lists the pump, tank and controls but not a contact tank or downstream filter, so ask what to pair it with before you order.

Chlorine, peroxide or permanganate?

All three are injected the same way. They differ in what they leave behind and how they’re handled. Penn State Extension’s notes on each:

Whatever the oxidant, the filter after it does the removal. If the filter is undersized or never backwashes properly, oxidized iron and sulfur pass straight into the house.

When chemical injection is the right tool

Penn State also notes that chlorine is not recommended for very high manganese because complete oxidation requires a very high pH. If manganese is your main problem, show your numbers to an independent water professional before you buy.

Bacteria: what injection can and can’t do

Continuous chlorination is one of the three continuous disinfection options Penn State lists, along with UV and ozone. To work, the water must be clear (a sediment filter is typically used), it needs a residual of about 0.3 to 0.5 mg/L, and it needs roughly 30 minutes of contact time.

Two cautions:

• Don’t jump straight here after one positive coliform test. Shock chlorinate, fix any well cap or casing defect, and retest. See shock chlorination.
• Iron bacteria are stubborn. The Minnesota Department of Health (MDH) says iron bacteria are not known to cause disease. MDH does not usually recommend continuous chlorination for them because it “may hide other bacterial contamination” and can cause corrosion. MDH favors shock chlorination and, for heavy growth, physical cleaning by a licensed well contractor.

If bacteria are your only issue and your water is clear, a UV system is usually simpler. More on bacteria in well water.

Where it goes in the treatment order

1. Sediment filter or spin-down screen. SpringWell’s manual recommends one ahead of its system and warns that sediment can interfere with the flow switch.
2. Shut-off valve, so you can service the equipment.
3. Flow switch and injection point.
4. Contact tank or pipe coil.
5. Backwashing filter to remove the oxidized particles.
6. Carbon filter to remove chlorine taste.
7. Water softener, after the iron is out, so oxidized iron doesn’t foul the resin.

Install needs

• Wall space and a stud. SpringWell’s manual says the pump must be mounted to a stud because of its weight.
• Floor space for the solution tank. SpringWell’s tank holds 35 gallons and measures 18 inches wide by 33 inches tall.
• Power. The pump plugs into the flow switch box, never straight into the wall. The box needs a nearby outlet.
• Drain for the backwashing filter downstream.
• Pressure and flow. SpringWell rates its system at 10 to 150 psi and up to 30 GPM service flow, with water from 36 to 104°F.
• Ventilation and safe storage for chlorine.

Maintenance

MDH lists the downside plainly: chlorination systems are complex, may take up a lot of space, and need frequent maintenance and monitoring. Expect to:

• Mix and refill solution. SpringWell’s guide uses 1 gallon of bleach to 34 gallons of drinking water for the first fill and says to refill when the tank drops below 5 gallons.
• Maintain the pump. Pump tubes wear and need replacement. SpringWell ships a replacement pump tube with its kit.
• Backwash and replace media in the downstream filter.
• Replace carbon when chlorine taste returns.
• Check chlorine residual with a test kit after the carbon filter and at the tap.

Safety. Penn State’s coliform guidance notes that chlorine is hazardous to handle. Wear eye protection, store it away from acids and ammonia products, and never mix bleach with other chemicals. MDH also notes chlorination may create by-products in drinking water, which is another reason for the carbon filter.

Who should skip it

• Moderate iron, manganese or sulfur. If your numbers sit inside an air-injection or greensand filter’s range, start with a whole house well water filter. It is far less work.
• A smell in the hot water only. That points to the water heater anode, not the well. See hydrogen sulfide in well water.
• One positive coliform result. Shock and retest first.
• Households that won’t keep up with refills. A dry tank means no treatment, and you may not notice until the stains or smell return.
• People who can’t tolerate any chlorine taste and don’t want to maintain a carbon filter.

For sulfur-specific comparisons of chlorine, peroxide and air, see SulfurWaterFilter.com.

When to call a pro

Get help from a licensed water treatment contractor if your water has very high manganese, if you need disinfection and iron removal together, or if you have no floor drain for the downstream filter. Bring a certified lab report, or enter your numbers at /test-results/ first.