Ultra Violet Dose

The most important factor in determining the effectiveness of a UV unit is the UV dose that the bacteria receive.  The UV light used to sterilize bacteria is the same UV light that gives us humans sunburns.  You won't get a sunburn just walking between your house and your car because you don't get enough of a UV dose.  Likewise, bacteria won't be sterilized by your UV unit if they don't receive a high enough UV dose.  So, what UV dose is needed to properly sterilize the types of bacteria commonly found in wells?

 Scientific studies tell is the necessary dose is 40 mJ/cm2.  The question, then, is whether the UV unit you are considering is rated at this 40 mJ/cm2 dose.  The answer can vary by jurisiction.

Let's say you are looking for a UV in Kingston, Ontario.  In Ontario, a minimum dose of 40 mJ/cm2 is required by law for UV equipment that is being installed at a public facility (school, daycare, restaurant, campground, etc.).  There is no law, however, governing the UV dose of UV systems for residential use.  Unfortunately, this has led to manufacturers arbitrarily rating the capacity of their residential UV equipment at lower UV doses than they actually should.  This lets them "magically" convert a unit with a capacity of 3 gpm in the regulated market to a UV unit with a capcity of 6 gpm or 10 gpm in the residential market for no extra cost. 

A consumer who is unaware of the issue of UV dose sees two units, both rated at 10 gpm, but at widely different costs.  Often they just pick the cheapest unit and unknowingly try to treat their entire home with a UV unit that is actually only powerful enough to treat a single tap.  Here at MacLellan Water Technology, we size our residential UV units at 40 mJ/cm2 with the thinking that the bacteria in your well are no weaker than the bacteria in the restaurant down the road despite what provincial law might seem to think!