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

Including a UV light treatment stage in your water system can be very effective at sterilizing your water, but at what point should the sterilizer be installed?  Here are a few simple guidelines to follow when installing a UV sterilizer that will help you get the most out of your system. GN-15 NSF UV Sterilizer

First, 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.

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

Typical installation with UV sterilizer
Typical installation with 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:


You can send any further questions regarding UV light and water systems to [email protected].

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