Wednesday, March 1, 2017

Top 6 Factors Affecting Ultraviolet Treatment of Well & Spring Water

Factors Affecting UV Treatment

Water to be treated by UV light should be clear and relatively low in minerals:

  1. Water should be low in hardness minerals: Less than 7  grains per gallon of hardness, or less than 120 PPM) 
  2. Water should be free of color 
  3. Iron should be less than 0.3 mg/L.   
  4. Manganese should be less than 0.05 mg/L
  5. pH range should be 6.5 to 9.5
  6. Turbidity should be less than 1 NTU

Pre-treatment Important Consideration

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 which will remove the hardness is recommended.  If the water is high in turbidity or cloudy, it is essential to treat the water prior to treating with UV light.

The UVT or UV Transmission level 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.

UV dosage is measured in microwatt-seconds per square centimeter area. From these units, it can be seen that UV dosage is a function of UV intensity (microwatts) and time (seconds). The industry standard of recommended UV dosage is 30mJ/cm2 30,000 µWt-secs/cm2.  This dosage is sufficient for most water-borne pathogens — 99.99 percent of E. coli will be removed with a dosage of 6-10mJ/cm2   UV sterilizers are sized in gallons per minute, in order to properly dose the water with the minimum UV dosage of 30mJ/cm2 30,000 µWt-secs/cm2.

By following the recommended maximum gallons per minute, and assuring the water is properly pre-treated, the UV system will perform properly.

Routine Testing

Water should be tested for coliform bacteria on a regular basis.  Home test kits are available that can show if coliform is present or not.

Pre-treatment System for Hard Water  

Water Softener > 25/1 Dual-Grade Filter > UV Sterilizer

Hardness (calcium carbonate) in water has a dramatic effect on how well UV sterilizers work. If the water is high in hardness (7 grains/gallon or greater) mineral scale will form on the quartz sleeve and prevent the UV light from properly reaching into the water.

Pre-treatment for Iron in Well Water

Iron Filter > 25/1 Dual Grade Filter > UV Sterilizer

Iron is common in many well waters.  If iron is present it will prevent the UV sterilizer from working properly.  

If the water is high in iron (0.3 PPM or greater) rust will form on the quartz sleeve and prevent the UV light from properly disinfecting the water.   Cloudy or rusty water will also inhibit UV transmission.

Pretreatment for Sediment in Well Water

Sediment Backwash Filter > 25/1 Dual Grade Filter > UV Sterilizer

Sediment, turbidity or cloudiness in water will affect how well the UV sterilizer can disinfect water. Sediment and/or cloudiness in water will prevent UV rays from reaching the edge of the UV chamber and reduce how well the UV can disinfect the water.   For UV to work properly, water should be low in turbidity (less than 1 NTU) and free of sediment.


Our company Clean Water Systems & Stores has been providing solutions for thousands of problem water wells since 1985.  Many folks contact us regularly asking about UV sterilizers, which can be a great alternative to traditional chlorination systems for disinfecting well and spring water.

We created guides to answer these questions in as simple as format as possible.  Questions answered include:

·         How does UV light disinfect water? 
·         How can I know if UV is right for my water application? 
·         Should the water be treated in any way prior to UV sterilization?
·         When should I hire a professional to do the installation and maintenance? 
·         Is it possible to maintain it myself or do I need special training?
·         What kinds of bacteria are killed by UV light?
·         Is UV light effective at killing parasites, such as Giardia?

If you have any questions about the material in this guide, or want to offer us feedback please contact us!

Toll-free:  888-600-5426   
Through our online support forum:

Clean Water Systems & Stores Inc
2806-A Soquel Ave
Santa Cruz, CA 95062