Ultraviolet equipment for the home comes in three formats that are frequently compared as though they were interchangeable. They are not: they differ in what proportion of the household's water they treat, and that scope, rather than any difference in the underlying technology, is what should decide the purchase.
Point of entry: the whole supply
A chamber plumbed into the incoming main treats everything: every tap, every shower, the washing machine, the ice maker. It is the standard arrangement on a private well where the supply itself is in question, and it is the only format that answers a positive bacteria result properly, because a positive result affects every fixture rather than one. It is sized on the household's peak simultaneous draw, needs pretreatment to keep the water clear, and needs an annual lamp change.
Point of use: one tap
A small chamber under a sink treats drinking water only, and it suits households who want a final barrier without work on the incoming main: renters, apartments, and anyone whose supply is generally trusted. It is much easier to fit and much cheaper. Its limitation is scope, and it is worth being blunt about it: showers, teeth cleaning and food washing at other sinks are untreated, so it is not an answer for a supply with a microbiological problem.
Batch devices: bottles, pitchers and countertop units
These illuminate a fixed volume for a set time rather than treating flowing water, which removes the flow rate variable that causes most plumbed system failures. They suit travel, camping with a prefilter, emergency kits and households wanting a final barrier on drinking water with no installation at all. They still need clear water, they still have a lamp that ages, and they treat only what is put in them.
Choosing, and the check that comes first
On a community supply, read the annual report before buying anything: the EPA notes every community water system publishes a Consumer Confidence Report and maintains a finder for them, and if the system is meeting its requirements a lamp is a barrier against a managed risk. On a well with a positive result, point of entry is the answer. On a well that is clean but you want reassurance, any format is defensible. Our home filtration cost guide covers what each adds to a system.
Questions people ask about uv water filtration systems for home
Which format do I need on a well with bacteria?
Point of entry. A positive result affects every fixture, so treating one tap leaves showers and other sinks untreated.
Are batch devices as effective?
For the volume they treat, yes, and they remove the flow rate variable. They cannot cover a household's whole supply.
Do I need any of them on city water?
Usually not. Read your utility's annual report first, since community supplies are already disinfected and monitored.
Do all three need pretreatment?
Yes. Ultraviolet needs water clear enough for the light to reach organisms, whatever the format of the device.