UV Water Purification Buyer’s Guide

Posted by
John Woodard on July 21, 2023

UV water purification systems come in different classes, types, and sizes, some of which are better suited for specific situations than others. For example, a home that uses well water requires more water disinfection than one that is connected to the municipal water supply. Regardless of your water source or home size, there is a UV purification system that best suits your needs. Below you can find information on the types of UV purification systems, how to size a UV system, and other tips on purchasing a system for your home.

UV water purification basics

A UV water purification system is used to decontaminate water that contains bacteria, viruses, and parasites. The most common application for UV water treatment is well water, but many homeowners opt to protect their municipal water from microorganisms in rare cases of contamination.

UV systems utilize a bulb that emits UV-C light, a specific wavelength of UV light that deactivates microorganisms. Once deactivated, these microbiological contaminants cannot reproduce and are no longer a threat. However, water feeding into a UV system should be as clear from contamination as possible. Minerals, sediment, and dirt block the UV light from reaching the microorganisms it must deactivate. Consequently, pretreatment systems, such as water softeners and sediment filters, are essential for successful UV water purification.

Learn more: What is a UV water purifier?

Does a UV water purifier treat water for a whole home?

Yes, UV systems are point-of-entry (POE) systems rather than point-of-use (POU), meaning all water that flows into your home is treated by the UV system. This ensures that all water used for drinking, cooking, brushing teeth, bathing, and other uses does not contain microbiological contaminants. If you want further treatment of water at a single faucet, such as one used for cooking and drinking water, consider a POU reverse osmosis system.

Learn more: What is a reverse osmosis system?

What size UV water purification system do I need?

UV systems are measured by flow rate, the number of gallons they treat per minute. The standard flow rate of a UV purification system is 8 gallons per minute (gpm). However, a large home will require higher flow rate systems to accommodate its water needs. You can best size a UV system by using the number of bathrooms for reference. For example, a 1-bathroom home can safely utilize a 6 gpm UV system. For each additional bathroom, 2 to 3 gpm should be added to the total. When in doubt, it is always better to oversize your system than to undersize it. A UV purification system that is too small for your home’s flow rate will not adequately treat water, leaving those in your home at risk of waterborne illness.

  • 1 bathroom – 6 gpm or greater
  • 2 bathrooms – 8 gpm or greater
  • 3 bathrooms – 10 gpm or greater
  • 4 bathrooms – 12 gpm or greater

Learn more: How to install a UV system

Does the flow rate of a UV system matter?

Yes, the flow rate of water through a UV system determines if water contacts the UV light long enough to deactivate microorganisms. Flow restrictors are an essential component to every UV system. If flow rate is unregulated through a UV system, water may pass through before it can be properly treated. Water that rushes through the system is not subjected to UV-C light for a sufficient period, leaving some bacteria and viruses active in the water. To ensure your UV system properly disinfects all water running through it, you must install a flow restrictor to the incoming plumbing. The flow rate of the water should at most match the maximum allowed flow rate of the UV system.

Learn more: What is a flow restrictor?

What prefilters does a UV system need?

To effectively treat water, a UV system requires pretreatment to remove sediment and minerals that cause the system to become less effective. The two key filtration components needed before UV purification are a 5-micron sediment filter and a water softener. A sediment filter removes suspended matter in water, such as dirt, sand, dust, and other debris larger than 5 microns. If left in the water, this debris can block UV light from optimally disinfecting water. Water-hardening minerals are also hazardous to a UV system’s performance. Water flowing through a UV system must be softened for the treatment to be effective. Consequently, a water softener should be used in conjunction with a sediment filter as pretreatment for your UV system.

Learn more: What is a sediment filter? | What is a water softener?

What is a UV purification system alarm?

A UV water purification system’s alarm signals when the sensor detects that something is wrong with the system. The alarm is an essential feature that indicates one of the following conditions:

  • The UV lamp must be changed.
  • The alarm must be reset (if lamp was already changed).
  • Water quality is not acceptable.
  • The quartz sleeve is cloudy.
  • Power issues must be addressed.

Learn more: How to maintain a UV system

Classes of UV systems

NSF/ANSI 55 separates UV water purification systems into two distinct classes, Class A and Class B. Class A UV water systems should be used with water that contains microbiological contaminants, such as well or surface water (streams, lakes, etc.). These systems are designed to inactivate microorganisms, including bacteria, viruses, Cryptosporidium oocysts, and Giardia cysts from contaminated water. Class A UV systems should not be used to treat raw sewage, wastewater, or any water with an intentional source. They are intended to be installed on visually clear (not colored, cloudy or turbid) water.

Class B UV water systems, on the other hand, should only be used as supplemental bactericidal treatment with water that is already disinfected. These systems are optimal for use with public drinking water or other drinking water that has been tested and deemed acceptable for human consumption by the state or local health agency having jurisdiction. Class B UV systems are designed to reduce normally occurring, nonpathogenic nuisance microorganisms only. These systems are not intended for the disinfection of microbiologically unsafe water and may not make individual or general cyst claims. Microbiological health effects claims may not be made on Class B systems.

Learn more: NSF Class A vs Class B UV Systems

What is UV dosage measured in?

UV dosage is the measurement of energy delivered by UV water systems, typically measured in mJ/cm². The higher the dosage provided, the greater the energy delivered to any microorganisms present in the treated water. At a certain threshold, this energy becomes sufficient to inactivate most of the microorganisms present.

What UV dosage is used to treat water?

Class A UV systems must deliver a dosage of at least 40 mJ/cm², while Class B UV systems must deliver a dose of at least 16 mJ/cm². The higher dosage of Class A systems allows them to inactivate pathogenic organisms, and the lower dosage of Class B systems allows the deactivation of only nonpathogenic organisms.

When this dosage is tested, the flow rate must match the system’s maximum acceptable rate. The UV Transmittance must also be reduced to 70 percent or to the alarm’s setoff point, whichever percentage is lower.



If you have any additional questions, please do not hesitate to contact us.


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