If you run a private well near Washington, you may have heard that an ultraviolet light unit takes care of bacteria in the water. It can help with that one job, but only when the water reaching it is already clear, and that depends on checks you make first.
What a UV unit does and does not do
A UV unit passes water past a lamp inside a quartz sleeve. The light is aimed at microorganisms as the water moves through the chamber. It does not remove sediment, iron, hardness, nitrate, hydrogen sulfide, or radium. It also does not clear cloudiness, change taste, or fix a problem that starts at the well itself. Think of it as one stage in a system, not a fix for everything.
Why pretreatment comes first
Cloudy or sediment-laden water can shield microorganisms from the light, so the unit may not reach them. Iron and mineral deposits can also coat the sleeve over time and reduce how much light enters the water. Private wells in the Franklin County area often run high in iron, so a sediment filter ahead of the UV unit is a common arrangement. Look at the water before you assume the lamp is working.
Checks before you touch the lamp
- Look at the water at a tap before it reaches the UV unit. Note any cloudiness, orange color, or grit.
- Check the sediment filter ahead of the unit. A dirty or clogged cartridge can reduce flow and let debris reach the sleeve.
- Confirm the unit has power and that its indicator light shows it is running. Note whether an alarm or warning light is on.
- Find the date on the lamp and compare it with the replacement interval in the manufacturer's manual. Do not rely on memory.
- Look at the quartz sleeve through the access port if your model has one. A film or deposit points to iron or hardness rather than a lamp fault.
- Compare the flow rating printed on the unit with your actual household use. Water moving faster than the rating gives the light less time with it.
Testing the water on each side
Private wells are not regulated, so testing is your job. A coliform and E. coli test from a certified lab is the usual starting point for bacteria. Take one sample from a tap ahead of the UV unit and another from a tap after it, so you can see whether the unit is making a difference. Ask the lab how to collect the sample and follow its steps closely, since a poor sample can give a misleading result.
After a flood or a long power outage
Flooding can carry surface water into a well and may bring bacteria with it. A UV unit should not be the only defense in that situation. If your well has flooded, or if power has been off long enough that the unit stopped, check the sediment filter, look for cloudiness, and arrange a bacteria test before returning to normal use. Public water reports for Washington describe a mix of river and groundwater, but a private well sits outside that system and needs its own testing.
When the lamp is not the problem
If the water looks clear and the lamp is recent, the cause may be upstream or in the plumbing. Hydrogen sulfide produces a rotten egg smell, iron leaves orange staining, and nitrate and radium can only be identified by lab testing. Each needs a different response. Write down what you see, smell, and taste, then match those observations to the right test instead of replacing parts at random.