Your don’t have a municipal water supply to your house.  The water comes from a well, and you’ve decided to protect the health of yourself and your family by installing a water treatment system.  You’ve done some research and have decided you want an ultraviolet light treatment system, because it uses no chemicals.  So how do you choose the most appropriate system for you?

Your very first condition is to find a system that provides a minimum safe dosage of disinfection.  After all, you want to make sure that you kill any organisms that might be in your water with a safe margin of error.  The way this is accomplished is by third party validation.  There are companies out there that test U.V. devices to make sure they can provide the most appropriate dosage. The strictest of these third parties, and the one that Canadian and USA governments base their regulations on is NSF, or the National Sanitation Foundation.  After extensive testing, NSF has come out with a standard for U.V. disinfection devices. This standard is NSF 55 Class A protocol.  NSF 55 Class A tells us that a minimum safe dosage for U.V. systems is 40 mj/cm2.

But that dosage is not just dependent on the ability of the unit to provide it.  It is also very dependent on the conditions of your home and the water supply.  There are two things that you must know when going shopping for a U.V. unit:

1. Your maximum flow rate
2. The U.V.T. (ultraviolet transmittance) of your water.

U.V. dosage is calculated by the energy of the lamps, your maximum flow rate, and your UVT, or how much U.V. light energy can pass through the water.

Estimating Flow Rate:

It is unlikely that every single tap and shower will be on and every toilet in the house will be flushed at once.  The larger your family is, the more water will be used.  To estimate the flow rate, simply observe your families habits on the busiest days of water usage.  Take a note pad and figure out when the most water is being used.  When you’ve done that, it’s time to see how much water flows.  For each outlet, turn it on and let it fill a measuring cup while timing it.  If it takes 10 seconds to fill up a 1 liter measuring cup, then your device can go through 6 liters per minute.  Add all this up to come up with a maximum flow rate.

Finding out your UVT:

This is not something you can do yourself. Also, it’s important to note that sometimes when water looks clear, it can have dissolved minerals and organics that can absorb U.V. light.  You need to send a raw water sample (raw water means before any existing filter or treatment devices) to a laboratory so they can test it for you.  This is a simple test and shouldn’t cost more than $20.00 to complete.  If you don’t know of any labs or are having trouble locating them in your phone book, contact your local health unit or municipality. They should be able to provide one for you.

Now you have the information you need to go shopping for a proper unit.  Don’t be afraid to ask questions, and don’t let the salesman tell you that you don’t need a dosage that high.  In most cases, the person selling you the U.V. system is just a salesman. While he may know a good deal about water treatment equipment, he does not have the knowledge, expertise or experience of the people at a company like NSF.  The NSF 55 Class A standard was derived from testing using live bacteria, and that is how they came up with this minimum safe dosage.  Tell the salesman your U.V.T, your maximum flow rate and the dosage you need, and insist you look at the specifications.  If your UVT is 75% and your flow rate is 60 liters a minute, and the specifications of the UV system say 50 liters per minute and require a UVT of 95%, that system is not adequate for your needs.

Other Requirements:

All U.V. lamps have a lifespan.  Most reputable manufacturers tell you to replace the lamps once per year.  All U.V. lamps start off strong when you first fire them up and slowly get weaker over that one year span.  You should ensure the manufacturer has based the minimum U.V. dosage at the end of lamp life, not at the beginning.

A U.V. system produces heat and will “cook” water just like a kettle if it is let stand too long.  And just like a kettle, some of the minerals in your water will come out as a white flaky material.  No doubt you’ve cleaned out your kettle and seen the hardness and limescale build up.  This can happen to your U.V. if there are periods where you let it sit for a long time, or leave it on while you go away on vacation. There are ways of mitigating this problem, and make sure you ask the salesman how this can be prevented. Remember, if the U.V. system is coated with white scale on the inside, non of the U.V. light will be able to do any disinfection.

Some U.V. systems come with alarms.  This can tell you if the lamp has degraded, your one year is up, or if the system is fouled with lime scale.  A good U.V. system will have a sensor that can determine these things and an alarm to alert you that the water is not being properly disinfected.  A high quality system will come with a shut off valve that will not allow any water to your house if it is not properly disinfected.

Remember, when it comes to the saftey of the water you and your family drinks, not all U.V. systems are created equal.  Make sure you have the right one for your needs, and you can rest assured your water will be safe to drink.

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