The concept of using ultraviolet (UV) light to purify water has existed for over one hundred years. Yet in spite of its early beginnings, the science behind ultraviolet light disinfection is rather complex. To understand the fundamentals of how UV light is able to purify water for drinking requires a somewhat deeper understanding of chemistry, physics and biology. In this article, the science behind disinfecting tap water using a UV water filter system is discussed.
When you speak of UV water filter systems, the amount of UV light used is typically called a dose. An ultraviolet dose is simply the amount of UV light an organism is exposed to when it moves through a UV water purification device. The good news is that it takes very little exposure to UV-C light for a microorganism to become unable to replicate. It is impossible to overdose ultraviolet light.
The end result of cell reproduction is two identical cells, each with a functional copy of DNA as well as all of the other necessary structures for the cell to function. This is true for human cells as well as for plants, animals and the bacteria and viruses that can sometimes be found in drinking water. For DNA to replicate, a special protein travels its length and splits it in half. Using the ladder analogy, this protein then travels down the ladder and splits each rung along the way. What results are two separate molecules that each resembles a side of a ladder. During normal DNA replication, the protein travels down the ladder and as each rung is split, each side is immediately rebuilt. What results are two identical strands of DNA; one for each of the resulting cells.
Ultraviolet-C light is able to penetrate through cells and attack the DNA inside them. UV-C actually fuses some of the rungs of the ladder together. After the DNA of a cell has been exposed to enough ultraviolet-C light and some of the DNA rungs have been fused, the protein that is responsible for splitting the DNA cannot do its job. As it encounters a fused rung, it just stops completely, and the replication stops along with it. This keeps the cell from being able to reproduce. Therefore, a viral or bacterial cell that can't reproduce is also not capable of causing an infection. To say it another way, if a viral or bacterial cell cannot reproduce, then it can't make anyone sick.
Manufacturers of UV water filter systems produce varying sizes of filters to address different water conditions and flow rates. A slower water flow rate means that the water that is undergoing treatment stays in the filtering system for a longer period of time. For systems with higher flow rates, a longer UV lamp is required to make sure that the dose of ultraviolet light is adequate.
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