Thursday, October 3, 2013

Should I Install an Ultraviolet Light System Before or After a Water Softener?

I have a water softener and whole house sediment filter I bought from Home Depot.  Recently our well water tested positive for coliform bacteria.  I shocked the well with bleach and waited a few weeks and retested our water, and now it came out clean, no bacteria.
However, my wife does not trust the water and we want to install a UV filter so all our water is always disinfected.  If I get one, should I install it before or after our water softener?
Longmont, CO


This is a good question. Water to be treated by UV light should be clear and relatively low in minerals.  If the water is hard (over 5 – 10 grains per gallon of hardness) a water softener is recommended to remove the hardness.  

Since you have a water softener, you should install the UV sterilizer last, after the softener.   

Illustration of a standard installation w/ UV sterilizer

If the water is cloudy or high in turbidity, it is essential to treat the water prior to treating with UV light.  The UV Transmission level ("UVT") should be low enough to allow the UV rays to penetrate the water.  A 5 micron filter for pretreatment is recommended as a minimum precaution.    

In some cases, if the well is under the influence of surface water, the water can be contaminated with parasites such as Giardia.  In that case, a 1 micron absolute filter is recommended prior to the UV sterilizer, or an ultra-filtration is recommended.

You can get a copy of our free guide to Ultraviolet Sterilizers by going to this page:

Thanks for the e-mail, and good luck installing your UV system!