UV Disinfection
UV Disinfection & Bacteria Treatment
A positive coliform result on a private well is a fixable problem — but UV only works on water that's already clear, which is why it always goes last.
At a glance
UV Disinfection- TreatsColiform, E. coli, cysts
- Dose≥40 mJ/cm²
- Lamp changeAnnually
- Chemicals addedNone
Figures are typical ranges for Massachusetts installations. Your system is specified from your own test results.
What a positive coliform result means
Total coliform bacteria are an indicator, not usually a danger in themselves — their presence means a pathway exists between the surface and your well, which is what needs attention. E. coli is different and means recent faecal contamination; that's a stop-everything result and calls for immediate bottled water and shock chlorination. Either way the first step is not equipment. It's finding the pathway: a failed well cap, a cracked casing, surface water intrusion after heavy rain, or a septic system too close to the well.
How UV works, and its one requirement
Ultraviolet light at 254 nanometres scrambles the DNA of bacteria, viruses and cysts so they can't reproduce. It adds no chemicals, changes nothing about taste or odour, and leaves no residual. The requirement is clarity. UV works by exposure, so anything that blocks light — sediment, turbidity, iron, manganese, tannins — shadows organisms and lets them pass through alive. A UV lamp installed on cloudy well water gives you a green light on the wall and untreated water at the tap. That is why UV is always the last stage, after sediment, iron and manganese have already been dealt with.
Maintenance is not optional
A UV lamp loses output long before it burns out. It needs replacing every twelve months even if it's still glowing, and the quartz sleeve around it needs cleaning on the same schedule — mineral film on the sleeve blocks the light just as effectively as turbidity in the water. Systems with a UV intensity monitor and an audible alarm are worth the small extra cost on a well, because a silently degraded lamp is worse than no lamp: you stop boiling water and you stop testing, because you think you're covered.
How it goes
Test first. Quote second. Install third.
In that order, every time. It is the only way to know whether you need a three-thousand-dollar system or a two-hundred-dollar one.
Free in-home water test
We measure hardness in grains per gallon, pH, chlorine or chloramine, iron and total dissolved solids at your tap, and look at your plumbing, water heater and any existing equipment. About 45 minutes, no obligation. Where it's warranted, PFAS, arsenic, radon and bacteria go to a MassDEP-certified laboratory — quoted before any sample is taken.
Straight answers, in writing
Every number read against its standard, what it means for your house, and what we'd do about it. Including the cases where the answer is that you don't need anything from us — which in MWRA communities happens often.
Installed, tested, and proven
Licensed, insured, permitted where your town requires it, and sequenced correctly: sediment, oxidation, softening, specialty media, then UV. We re-test after commissioning, because a system nobody verified is a hope rather than a treatment.
Straight answers
UV Disinfection — common questions
Does UV remove chemicals or metals?
No. UV is exclusively a disinfection step — it inactivates living organisms and does nothing to arsenic, lead, PFAS, iron, nitrate or hardness. It's one stage of a system, never the whole system.
Do I need UV if my test came back clean?
Not necessarily. Many Massachusetts wells test clean year after year. Homeowners choose UV when results have been intermittent, when the well is shallow or in a flood-prone spot, when there's a septic system nearby, or simply for peace of mind with young children or an immunocompromised family member in the house.
What happens during a power outage?
The lamp goes out and water passing through is untreated. Most quality systems include a solenoid valve that closes the line when power is lost, so untreated water can't reach the house. We'd recommend that on any well where coliform has ever been detected.
Free in-home water test
Let's find out whether you actually need this
The in-home test is free, takes about 45 minutes, and ends with a written report — including the parts where the answer is that you don't need anything from us.
- Hardness in grains per gallon, pH, chlorine or chloramine, iron and TDS — measured at your tap.
- PFAS, arsenic, radon and bacteria through a MassDEP-certified laboratory, quoted before any sample is taken.
- Every number read against its standard, in writing, with no obligation.
Request your test
2 minutesWe'll be in touch shortly to confirm a time for your free in-home water test. If it's urgent, call (508) 686-1582 and we'll pick up.