According to the U.S. National Institutes of Health, microorganisms in biofilms are responsible for over 80% of bacterial infections, with opportunistic pathogens in water system pipelines contributing to widespread waterborne dissease. in humans. In 2010 alone, these infections led to over 90,000 hospitalizations in the US and an economic impact of $855 million annually.
Preventing biofilm formation in reservoirs used to hold treated water for rapid on-demand use not only protects consumers, but it also protects hardware used in these systems and distribution networks. Over time, biofilm layers build up, a process known as biofouling, which blocks flow channels and leads to operational problems.
But designing a system to treat drinking water and one to prevent biofouling require completely different approaches.
Understanding the difference between treatment and maintenance
Water treatment or disinfection occurs when as water flows through a reactor system, where a combination of filtration and UV is applied to reduce the active microbes in the water. UVC LEDs are strategically placed within the water flow path, allowing the water to be exposed to the germicidal UV radiation as it passes through—this is the UV dose. For example, to achieve a 4 log reduction of E. coli requires a UV dose of 12 mJ/cm2. To achieve this in a water treatment system with a flow rate of 2 liters per minute, it would require about 120 mW at 265 nm with a 3-second exposure.
However, when calculating the power required to maintain disinfection in a tank, there are several variables that can control the efficacy—from the tank design to the materials. The dose required to maintain a level of disinfection in water post-treatment will be significantly lower than to take untreated water to a specific disinfection level. Additionally, while continuous exposure is used in treatment of flowing water, studies have shown than pulsed UV can be more effective at controlling biofilms. This makes UVC LEDs a more suitable approach than UV lamps for these applications.
Here is where the difference between water treatment and maintenance becomes especially important. Water maintenance refers to the storage of water that has already been treated and disinfected. While UVC LED-based disinfection effectively treats water as it flows through a system, water maintenance measures are necessary to maintain the quality and safety of stored water over time – water sitting in a reservoir or tank before being dispensed in a beverage system.
For instance, if a 1-liter tank is designed tall with a UV reflective material like polished aluminum or stainless steel, then this dose can be achieved in a little over 1 minute with a single 80 mW LED. However, if you have a wider tank design you may need closer to 3 minutes with the same materials.
Table 1 shows the range of doses achieved with an 80 mW LED at 265 nm. Non-reflective surfaces could include plastics with fillers or pigments, where polished metals can provide anywhere from 33% to 70% reflectivity for stainless steel and polished aluminum respectively.
Table 1: Calculated dose matrix for various reservoir tank designs and dosing periods.
| Exposure Time (minutes) | Dose Achieved on Non-Reflecting Surface | Dose Achieved with Reflective Surface (ave. 50% reflectivity) | |
| Tall 1L Tank | 3 | 6 mJ/cm2 | 30 mJ/cm2 |
| 1 | 2 mJ/cm2 | 10 mJ/ cm2 | |
| Wide 1L Tank | 3 | 3 mJ/cm2 | 20mJ/ cm2 |
| 1 | 1 mJ/cm2 | 7 mJ/ cm2 |
These calculations assume that the LED is turned on every 5 to 6 hours, or whenever new water is added to the tank. Tank design and materials can greatly impact the ability to meet dosage goals with a single LED, so designers must make trade-offs in the materials and tank dimensions to meet the goals of the application.
When designing a solution for water maintenance, design engineers must consider not just how to treat water, but how to maintain its quality after treatment. These are fundamentally different challenges that require distinct design strategies. While water treatment focuses on achieving disinfection targets during flow, maintenance demands a thoughtful balance of tank geometry, surface materials, and LED placement to sustain water quality over time.
By leveraging the flexibility of UVC LED technology, designers can tailor both treatment and maintenance systems to meet application-specific requirements—whether it’s rapid microbial reduction in a distribution system, or preserving disinfection in a static reservoir. In doing so, they can reduce energy use, extend system life, and safeguard public health.