Ultraviolet systems all use the same principle, so choosing between them is a question of arrangement rather than technology: where in the house the lamp sits, how large a dose it is built to deliver, and how it tells you when it has stopped delivering it. Those three choices follow directly from why the household is treating the water in the first place.
Point of entry against point of use
A point of entry lamp treats everything coming into the house, which is the standard arrangement on a private well where the concern is the supply itself. Every tap, shower and appliance gets treated water, and the unit is sized for the whole house peak draw. A point of use lamp sits under a sink and treats drinking water only. It is smaller, cheaper and easier to fit, and it makes sense where the supply is generally trusted and the household wants a final barrier on drinking water, or where a rental will not allow work on the incoming main.
The two duty classes
Units are offered in a higher grade intended for water known or suspected to be contaminated, delivering a larger dose with intensity monitoring, and a lower grade intended as a supplementary barrier on water already believed safe. The distinction is not marketing. A well with a positive bacteria result, a spring, or any source that surface water can reach needs the higher grade. A household on a chlorinated municipal supply adding ultraviolet for reassurance is in the second case. The EPA notes every community water system publishes an annual Consumer Confidence Report, which tells you which case you are in.
What all of them need to work
Whatever the arrangement, three conditions are common. The water must be clear enough for light to reach organisms, so pretreatment for sediment, iron and color comes first. The flow must stay within the unit's rating, because dose falls as flow rises. And lamp condition must be monitored, since a lamp glows long after its useful output has gone. A system missing any of the three is producing reassurance rather than treatment, and it will do so silently for years unless somebody tests the water.
Running costs and the annual job
Ultraviolet is cheap to run and cheap to maintain compared with chemical disinfection, and it adds nothing to the water, which is much of its appeal. The commitment is an annual lamp change with a sleeve clean at the same visit, plus whatever the pretreatment stages need. Budget for the lamp every year regardless of how the unit looks, keep a spare o-ring, and retest the water after installation and periodically afterwards. Our well water filtration guide sets out how the ultraviolet stage is ordered against the rest of the train.
Questions people ask about uv water purification systems
Is a point of use UV unit enough on a well?
Usually not. If the supply carries bacteria, every tap and shower is affected, so the lamp belongs at the point of entry rather than under one sink.
What is the difference between the two duty classes?
The higher grade delivers a substantially larger dose with intensity monitoring for water known or suspected to be contaminated; the lower is a supplementary barrier on water believed safe.
Does UV add anything to the water?
Nothing at all. There is no chemical, no residual and no taste change, which is both its main advantage and the reason it offers no protection downstream.
What does it cost to keep running?
A lamp every year, an occasional sleeve o-ring, and modest electricity. The larger ongoing cost is usually the pretreatment filters that keep the water clear.