Photo of a UV light water sterilizer - ugh UV Light Systems for Water Treatment of Contaminated Drinking Water

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UV Water Purification Systems guide:

Here we explain procedures & reasons for using permanently-installed UV light (ultra violet light) treatment systems to address bacterial contamination in drinking water or well water - one of the options for correcting unsanitary or unsatisfactory drinking water.

We discuss the following: How does an ultra violet light fixture correct bacterial contamination in well water? How do UV lights work? Details of proper UV light installation and maintenance for well water treatment. Water treatment methods for contamination, bacteria, lead, minerals, etc. Water treatment choices for odors, smells, sediment, cloudiness. Choices of types of water treatment equipment.

This series of articles explains many common water contamination tests for bacteria and other contaminants in water samples.

In these articles we describe what to do about contaminated water, listing common corrective measures when water test results are unsatisfactory. We include water testing and water correction measures warnings for home owners and especially for home buyers when certain conditions are encountered, with advice about what to do when these circumstances are encountered.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

UV - Ultraviolet light as a Water Purifier - Installation, Inspection & Maintenance Guidelines for UV Water Treatment Systems

UV Disinfection system (C) Daniel FriedmanUV water treatment systems used to disinfect drinking water combine the following components:

For the UV treatment system illustrated in most of the photographs in this article, at a U.S. property in New York we installed a Siemens Ultraviolet Water Disinfection System (formerly produced under the name Sunlight systems) shown in the photograph at above/left.

The UV disinfection system is installed either in a kitchen or point of use, or when protecting a whole building it is installed where water leaves the well pump and pressure tank and enters the building, so that water flowing through the disinfection system is exposed to a UV lamp to carry out the water disinfection process.

The "UV" light can indeed kill bacteria in water, provided that the flow rate of water through the device is not too fast (needs exposure time) and provided that the water is not too obstructed with sediment and provided that the light source is cleaned - the bulb needs to be changed periodically.

Steps in a Proper UV Disinfection System Installation

Our photograph (below) of UV disinfection system equipment and the water softener and filters required for effective UV treatment are from a water treatment system installed by Norberg Godinez in 2017 at a property in San Miguel de Allende, Guanajuato, Mexico.

UV water disinfection system San Miguel de Allende (C) Daniel FriedmanFor an effective water treatment system in an area where water is hard (high in minerals), to protect piping and water heating equipment as well as the UV disinfection system, city water is passed through the following sequence:

[Click to enlarge any image]

1. Water from the rooftop water storage tank passes through

2. A Grundfos® SCALA2 water pressure booster pump to lift water up and through water treatment equipment as well as to provide improved building water pressure, through

3.A sediment filter (to prevent debris-blocking of the water softener and later of the UV disinfection light)

4.A charcoal filter (to remove colors, odors in water and for added filtration) then through

5. A water softener (not shown) to remove minerals, principally calcium and magnesium, then

6. Through the Aqua Plus™ UV disinfection light (size chosen for a whole-house treastment system) and finally

7. To the building plumbing fixtures including both cold water and hot water provided through a tankless water heater that is also protected from scale blockage by this system.

Requirements for Effective UV Water Disinfection

AquaPlus UV Water Disinfection Light Data Tag (C) Daniel FriedmanHow do we know the UV light is properly installed and effective in treating drinking water?

If you are relying on a UV light to treat bacterial contamination in drinking water these considerations apply:

Power requirements for a UV disinfection light (C) Daniel Friedman


Disinfecting building piping (C) Daniel Friedman Disinfecting building piping (C) Daniel Friedman

Maintenance Instructions for UV Light Water Disinfection Systems

UV disinfection light operation (C) Daniel Friedman UV disinfection light operation (C) Daniel Friedman

UV light bulb cover being removed to confirm bulb is working (C) Daniel Friedman UV light bulb cover removed shows that the UV bulb is working (C) Daniel Friedman

Above: we illustrate removing the black plastic cap to give access to the AquaPlus UV light bulb chamber. This inspection port permits confirmation that the UV bulb is "lit" or working, though it may not indicate whether or not the bulb or chamber needs to be cleaned of sediment.

With the extensive protection of filters and water softening equipment described above we don't inspect this UV light, in San Miguel de Allende, to require frequent cleaning. The inspection for lit UV bulb can be most-safely done using a cellphone camera that gives a good view without direct exposure of the inspector's eye to a strong UV light.

What Contaminants are Removed by a UV Light Water Treatment System

Photo of a UV light water sterilizer - ughNothing is removed from the drinking water, but if the system is working properly, the UV light will kill bacteria in the water supply. The dead bacteria, along with other water contaminants (if there are other contaminants in the drinking water) are not removed by the light.

OPINION: Property sellers often install this quick and least-expensive "solution" in the course of a real estate transaction in order to meet the minimum requirements of a buyer's lender to provide "potable water."

Since the lending bank usually requires only a bacteria test as a measure of water potability, the new owner/residents may not know whether or not there are chemical or other contaminants in the water supply. When a UV light has been installed on a water supply, our recommendations for further diagnostic testing are outlined just below.

Look For the Source of Bacterial Contamination in a Well

Since one of the most common ways that bacteria enters a well is through a defect at the pitless adapter (joining the water pipe to the well casing) or at a buried well cap that is leaky or open. In such cases the presence of bacteria in water is really an indicator of ground water leakage into the well.

Surprisingly we have found significant non-coliform bacteria levels in well water traced to

Spiders living in the top of a well casing: the spiders eat insects, dropping flies or other insects into the well casing, a possible source of un-wanted bacteria.

Dead animals in the well? On occasion a mouse or other small rodent falls into a well casing, causing temporary contamination.

Well contamination sources such as these are easily corrected by sterilizing the well and its casing interior.


Should You Test for Other Contaminants in Well Water?

If ground water or surface runoff have been leaking into a well, this means that anything that is on the ground or in the soil around the well is likely to be entering the water supply. So treating for bacteria may be failing to address other contaminants. Further testing for other contaminants would be appropriate if a well fails a bacteria test.

In particular, if the well is located at a property where chemicals are likely to have been applied nearby, such as near an orchard, farm property, animal barns or pens, or where pesticides have been in use, or close to a gas station, or where other contaminants are known to have been in local ground water, tests for those specific contaminants are a good idea.

If a property is in a residential neighborhood that has not included farms, orchards, barns, gas stations, or nearby industrial processes, the chance of finding these other contaminants in a well is certainly much less.

See WATER TESTING ADVICE for an outline of when to test for what contaminants in well water.

See WATER TESTS for CONTAMINANTS for a list of articles on water contaminants and water tests.

Advice for Testing Water Systems after UV Light Installation

Often conditions cause for follow-up water testing after a UV water treatment light has been installed. For example a property owner may discover bacterial contamination in the water supply when a home is being sold. If the initial water test shows that the starting bacteria count is low - just a few CFU's/L, and if there is no reason to have concerns for other water contaminants, testing for bacteria again after the UV light has been installed is proper procedure, and should produce acceptable results.

Here are some post-UV-light installation water testing considerations:

What if the UV Light is Installed Without a Water Filter?

A reader recently asked for advice for a case in which the UV installer forgot to install the water filter. The water filter was to be re-installed the next day, but the homeowner had already observed a lot of debris coming out of faucets in the building after the new UV light was installed.

That high level of debris may have been due to disturbances of piping and water tank during the plumbing work, or the incoming water supply might simply be high in debris and sediment.

Actually, flushing out the plumbing system before re-installing the cartridge in the water filter is not a bad idea because often during plumbing work lots of extra debris is stirred up or even introduced into the system. But the filter needs to be in place to protect the UV light from becoming obstructed.

We advised the following for this case:

If the person taking the sample fully flushes the system and piping before collecting the water test sample it is likely to "pass" with acceptable results (in most U.S. communities that's a count of less than 1 CFU/L or in a "presence/absence" test, with a result of "absent").

When we recently installed a UV light water treatment system, preceded by a whole house filter (which is important for UV effectiveness as it keeps debris off of the bulb), we also sterilized all of the house piping using the well shock procedure at WELL CHLORINATION & SHOCKING.

The reasoning is that having been running a building plumbing system with bacteria in the water supply, there might be pockets of bacteria in debris trapped in the system.

In the particular case under discussion, the water test for a home buyer was planned for the day after the water filter was to be installed. Thus the home owner would not have time to go through the well shocking procedure in time for the water test.

Therefore the homeowner needs to either


If it does not, then go through the well shock procedure as described and things will either be just fine, or the UV system is not properly installed or not properly working.

Limitations of UV Disinfection Systems for Drinking Water

Watch out: Factors that affect the effectiveness and operating time of any UV light used to treat water in an effort to make it potable, or at least improve its potability include at least the following:

Using UV light in a wide range of applications including the control of bacteria, mold, and algae or moss growth is also discussed at UV LIGHT BLACK LIGHT USES


Continue reading at WATER TREATMENT EQUIPMENT DISINFECTION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see UV WATER DISINFECTION, PORTABLE for emergency or camping use



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UV ULTRAVIOLET LIGHT WATER TREATMENT at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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