Sizing a UV Water Disinfection System the Right Way
Written by: Gene Fitzgerald // Last Updated: Dec 14, 2022
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Adding a UV water purifier to your plumbing system can boost your household’s water quality by killing bacteria and other microorganisms in your water. However, not all UV water disinfection systems are equally effective. The right system for one home might not be perfect for another.
This guide will help you choose a UV water purifier by explaining how to size one for your household. It also covers other factors you should consider when choosing, ensuring you’ll know how to find a disinfection unit that suits your needs.
Contents
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Key Takeaways
- Your household’s size will determine the ideal size for your UV water disinfection system.
- Choose UV lamp size/intensity based on the types of microorganisms found in your water. For proper water disinfection, you need to make sure that required UV doses are met.
Sizing a UV Water Disinfection System
So, how do you size a UV water disinfection system?
Well, there’s no one “right” size for a UV water purifier. When choosing one for your home, you need to check your required flow rate and UV dose.
Step 1: Required Water Flow Rate
You need to consider your household’s size when determining what flow rate you need. The following rules of thumb will help:
- A flow rate of approximately 10 gallons per minute can provide water for 1 to 3 typical bathrooms.
- A 15 gpm flow rate can serve 4 to 6 bathrooms.
- If you need enough water for 7 or more bathrooms, a flow rate of 20 gpm is ideal.
Step 2: UV Dose (Level of Disinfection)
For proper disinfection, the water that flows through your system must be exposed to a sufficient amount of UV light for a sufficient amount of time. That means your flow rate — the amount of water that can flow through the system in a certain timespan — influences the size your system should be.
Essentially, if the flow rate is fast, with large amounts of water flowing through the system fairly quickly, you’ll need a relatively strong and large UV lamp.
How strong exactly depends on the type of germs present in your water supply. Bacteria and cysts are the easiest to kill. As such, they require relatively low UV doses. Viruses are a little harder to eliminate, followed by molds and algae.
| Germ Type | Required UV Dose (Estimate) |
|---|---|
| Crypto/Giardia Cyst | 10 mJ/cm² |
| E. Coli | 10.8 mJ/cm² |
| Legionella Pneumophila | 6 mJ/cm² |
| Hepatitis B Virus | 21.9 mJ/cm² |
| Penicillium Digitatum (Mold) | 26.1 mJ/cm² |
| Green Algae | 36.6 mJ/cm² |
The U.S. Department of Health and Human Services has established a UV dose of 16 mJ/cm² as the minimum threshold necessary to kill most common types of potentially harmful pathogens in water. That said, for more thorough disinfection, you may opt for 30 mJ/cm² or higher.
Other Factors to Consider When Choosing a UV Water Purifier
The flow rate and UV dose are two factors to always consider when sizing a UV water disinfection system. You should also keep in mind such factors as:
Water Quality and Pre-Filtration
Before buying a UV water purifier, have your water tested to ensure it meets these conditions:
- Hardness < 7 grains per gallon (gpg)
- Iron < 0.3 ppm
- Manganese < 0.05 ppm
- Turbidity < 1 NTU
- Tannins < 0.1 ppm
If it doesn’t meet those conditions, UV disinfection may not be effective, as the microorganisms the UV light is meant to kill could literally “hide” behind particles in your water.
Install a pre-filtration system to remove these particles if your water doesn’t meet the conditions above. Even if it does, adding a pre-filtration system will further optimize your water’s quality.
NSF Certifications
Check a UV water purifier for NSF and ANSI certifications before purchasing it. If a UV water disinfection system is certified, this indicates it meets basic standards and therefore is likely to work as intended.
- NSF/ANSI Standard 55 Class B certification indicates a UV water purifier can reduce the presence of bacteria that aren’t disease-causing.
- NSF/ANSI Standard 55 Class A certification indicates a UV system can kill or render harmless bacteria and viruses in your water.
Installation
Research ease-of-installation when choosing a UV water purifier. Although you shouldn’t settle for a low-quality system merely because it’s easy to install, you should feel confident you can hook up your chosen system properly.
Be aware, some systems come with warranties that may be voided if you don’t hire a professional licensed plumber to handle the installation.
Further Reading:
Space Requirements
UV water purifiers often aren’t very large. Still, you should consider space requirements when purchasing one. Check the UV system’s dimensions, and confirm you have at least double that amount of space. You’ll need additional space if you also plan to add a pre-filter.
Price
You need to consider your budget when purchasing a UV water purifier. That said, you also need to consider that the sticker price isn’t the only factor influencing the system’s overall cost. Other factors to account for include:
- Leakage: A seemingly budget-friendly system might be prone to leaks.
- Lamp life: The industry standard lifespan for a UV lamp is 9,000 hours of functionality. A cheap lamp may not last this long and will thus need to be replaced more often. This can add to your system’s cost over time.
- Lamp sleeve quality: If a UV water purifier is inexpensive, its quartz lamp sleeve might be low-quality. Such a sleeve may break more easily.
Essentially, you should prioritize buying a quality system. Doing so can actually save you a lot of money in the long run.
If you have any questions about sizing a UV disinfection system please don’t hesitate to leave a comment below!
About the Author Gene Fitzgerald
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