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Why Use UV light for Rainwater Harvesting

July 13, 2021

Why do we use UV light for rainwater harvesting systems?
An ultraviolet bulb is central to the more extensive filtration system we install with every potable rainwater catchment system

While it’s true that rainwater is soft and more pure than well water (i.e., lower in dissolved minerals such as iron and sulphur), there is always a chance of bacterial contamination with any body of water. Rainwater, when left untreated, can contain pathogens such as salmonella, giardia and, E.coli. The last thing we want to do is bring water into our homes that could result in a bellyache or severe illness. 

But we also prefer to avoid adding substances like chlorine to our harvested rainwater. This is exactly why we use UV light for rainwater harvesting. When we pass rainwater over a protected UV bulb, we ensure safe, chemical-free drinking water. This water remains soft, unadulterated by salts or groundwater minerals, easy on skin and appliances, and extremely safe to drink. There is no change to the taste or odor of your water. And just as importantly, you don’t have to handle noxious chemicals, monitor chemical levels, or worry about running out of chemicals to treat your water.

It’s good to keep in mind the size of a UV light is essential to the integrity of a potable water supply. When we are designing a rainwater system, we determine UV size based on several factors, including:

  • # of bathrooms are in the home
  • # of people live in the house
  • # of days out of the year the home is utilized

The UV and filter system we most commonly install is the Viqua E4, Pro UV Water Filtration System. At 22 GPM (gallons per minute), the E4 easily serves larger homes and small businesses.

rainwater filter board set up, Why use UV light for rainwater harvesting
Pictured above is a Harvest Rain set up for a filter board and includes (from left to right) a sediment filter, a carbon filter, and a UV bulb. The UV bulb is housed in a stainless steel enclosure. This is a Viqua E4 system and currently serves a family of 5.

As rainwater system designers we are intimately aware of why and how ultraviolet light helps protect our water. But we also hear a lot of misinformation about its effectiveness and application. Read below for four of the top UV myths we hear most often.

MYTH: UV kills bacteria.

A common misconception is that ultraviolet light kills bacteria and viruses. However, ultraviolet light doesn’t cause death but rather disruption. Via electromagnetic energy, ultraviolet light disrupts the microbe’s nucleic acids (DNA & RNA), preventing them from reproducing and thereby rendering them harmless.

MYTH: As long as the light is shining, the UV is working. 

The majority of UV lights we include in our systems are designed to provide consistent and reliable UV output for 9,000 hours (one year of regular use.) Although the bulb will continue to shine past 365 days, the intensity of the lightwaves will begin to diminish. You can expect your UV bulb to gradually lose at least 20% of its effectiveness every three months past its expiration date. Our best recommendation is to change your bulb annually and on time.

The Viqua E4, Pro UV Water Filtration System comes with a convenient display that counts down the days remaining on your bulb and audibly alerts you to change it. Learn more about Viqua’s line of UV products here.

MYTH: UV light can antibacterialize murky water.

No, ultraviolet light cannot disinfect murky water. In fact, water must be clear for UV rays to do their job. This is the reason why filtration before the light is so critical. To ensure the UV light receives water free of debris (think dust or pollen from your roof), we have several stages of filtration designed into each of our systems. You will always find a sediment and carbon filter paired with a UV light with any Harvest Rain potable rainwater system. These filters remove small particulate, maintain water clarity and ensure consistent water pressure. 

MYTH: UV bulbs take a ton of electricity to run. 

Nope. Residential UV light kits require minimal electricity for how much work they do (on average, they use about the same amount as a 40w light bulb). The light kit only requires a standard 115V outlet. However, when possible, we recommend dedicating a circuit for your rainwater filtration system. 

Do you have questions about how to upgrade your rainwater disinfection system? Contact our service team today by filling out the form below.

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