Ultraviolet UV Water Purification And How It Works


A highly effective method for home water disinfection. A ultraviolet light (UV) system.

It’s technically not a water filter. It doesn’t filter out anything by ‘capturing’ particulate contamination in a filter media. Rather, a UV (Ultraviolet) works by ‘zapping’ organic pathogens that may be in the water supply.

The method (the science) even works by natural sunlight (albeit much slower).

[ Read: How To Purify Water With Sunlight ]

How It Works

UV (ultraviolet) light ‘inactivates’ pathogenic micro-organisms. The UV light disrupts their DNA. They can no longer reproduce.

In fact, the method has been around for many years. ‘Developing’ countries around the world use the ‘SODIS’ method for water purification. (Solar Water Disinfection).

The WHO, UNICEF, and the Red Cross recommends SODIS. All it requires is sunlight and PET or clear glass bottles. How does it work? Fill Clear bottles with water and set them out in the sun for 6 hours. The UV-A rays in sunlight kill germs (e.g. viruses, bacteria, parasites, giardia, cryptosporidia).

SODIS taken to the next level…

The same principle is now being applied via ‘high-tech’. Ultraviolet (UV) lamps achieve the same results of water disinfection. But much quicker! Nearly instantaneous. They emit UV-C or “germicidal UV” radiation of much greater intensity than sunlight.

Geek alert: Almost all of a UV lamp’s output is concentrated in the 254 nanometers (nm) region in order to take full advantage of the germicidal properties of this wavelength.

These UV lamps are made in varying sizes. Some are designed for portability / water bottles:

>> UV Water Filter Bottles
(view on amzn)

…or whole-house UV water systems

>> UV Water Filters – Whole House

 Other types of water purification systems use chemicals or very fine screens to clean water. While these methods are effective, bacteria and viruses can slip through all but the finest screens. Apparently no known bacteria or viruses are immune to ultraviolet light.


If your water is turbid (cloudy). The UV disinfection will be inhibited to an extent. Cloudiness from solids in the water may protect the bacteria and viruses from the ultraviolet light.

Consider installing a sediment filter (5 microns or less) ‘upstream’ from the UV system.

If your water hardness over 7 grains, you should install a water softening device in front of your unit. Hard water will eventually leave a calcium/magnesium film which may reduce or block the UV rays.

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  1. Use UVC light for your water, your air, and to sanitize objects and entire rooms. These lights are long lasting, too.

    If one wishes, one may design their own systems specifically for their needs, as all the components required are on the shelf and available. This would allow one to chose the very best components, instead of letting maker do it for you. Building your own UVC system should also be less expensive.

    I use UVC to sterilize the air in my HVAC system, which also prevents mold development on its heater-A/C coil.

  2. In one of my resource books, a suggestion to extend filter life when you have particulates in the water is to 1st filter the water through a double thickness of t-shirts or similar material into a food grade bucket. Would that also help clear the water for UV?

    Another observation was to let the water sit overnight so particulates settle. Then carefully remove clearer water on top. I have tried this and was never careful enough to not stir up the settled matter.

    1. MamaLark ,
      research the SODIS System on the internet. They use it to help purify water in third world countries. Its using the sun’s UV Rays and recyclable water/soda bottles.Water doesn’t get hot enough to cause plastic leaching .(what most people worry about.)
      Actually freezing water bottles can cause plastic leaching.
      I have personally used this system for weeks as a test before I taught it to others.
      It’s a passive system that does work if your UV System goes down…

  3. UV water filter lights are very expensive for human consumption standards. A cheaper method that I use is for fish water treatment. Same idea, but much cheaper parts. Some of the pond water UV lights are all stainless steel with the same bulb and purpose, just for fish. Same idea goes for Reverse Osmosis systems.

    1. @ not so sure,
      Expensive is a relative term. For portability, we’re looking at about 20 bucks (and/or higher). For whole house, we’re looking at about 150 (and/or higher). And in both cases they are purpose built/designed as such. The technology is sound. I like to know about multiple ways and methods for safe drinking water. This is just one of them.

    1. Mrs. U,
      the sodis system using the sun varies with how many hours of unobstructed sunlight is available.
      Cloudless days is about 6 hours. Longer with cloud cover.
      Usually in the third world countires they have 2 sets of water/soda bottles per family. They put them on metal roofing in the morning. They come the next morning take the first set and replace them with the second set for the following day’s use.
      You need to strain any leaves,debris and dirt out of the water to be treated before putting them in the sun. They normaly do it through cloth. Reason being the viruses can survive the sun’s UV rays ” hiding” in the dirt or debris. The water reaches sufficient temperature in the bottles long enough to kill Giardia as well.
      You can google it and they have info and directions to download.
      The death rate from water borne illnesses in these countries dropped dramatically if done properly.
      Hope that helps…

    2. Mrs.U,
      The UV technology referenced in this article uses electricity (or batteries), so clouds are not an issue ;)

      I have a link in the article above, how to purify water with sunlight. Some answers are in there regarding SODIS.

      Regarding the count number of comments, it’s off because a thread got automatically deleted due to a lot of down-votes on a particularly poor comment.

      1. Ken,thanks for clarifying that. I only mentioned it because some folks may not be able to afford a UV System. It’s good information for folks to put in a folder just in case.
        I met a family who were stuck in Puerto Rico after the hurricane. No power,no running water,no fuel to boil water. The father got very sick from drinking bad water. If he had known about sodis system he most likely wouldn’t of got sick…

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