How to Purify Water With Ultraviolet Light

Ultraviolet light can be used to make drinking water safe.

Using ultraviolet light to purify water has many advantages. Once you have all the components for the system, you can purify large amounts of water fairly quickly and at a low cost. Other types of water purification systems use chemicals or very fine screens to clean water. Bacteria can become immune to chemicals and viruses can slip through all but the finest screens. No known bacteria or viruses are immune to ultraviolet light. In addition, many other water purification systems require pumps either as the primary filtration or to remove the added chemicals once the water has been purified.

Things You'll Need

• 5 micron or less sediment filter
• Latex gloves
• Clear quartz sleeve
• Mercury vapor lamp
• Rubbing alcohol

Instructions

1. Use the sediment filter to remove any sediment from the water to be purified. Any cloudiness from solids in the water may protect the bacteria and viruses from the ultraviolet light. Depending on the initial quality of the water, several filtrations may be needed. A carbon filter may be needed for very unclean water.

2. Choose your UV light source. A mercury vapor lamp will give the best wavelengths of UV light to kill viruses and bacteria. Mercury vapor lamps can be purchased from many hydroponic equipment suppliers, water filtration companies and home improvement stores. A quartz crystal sleeve should also be used because it filters the light for maximum effect against microorganisms and protects the lamp. As the lamp heats up, any oils or liquids that come in contact with the lamp will heat up and cause the lamp to give reduced and/or altered wavelengths of light, reducing its effectiveness. The sleeve can be purchased at the same places the lamp is sold and at some lab equipment companies.

3. Put on gloves before handling the quartz sleeve and the mercury vapor lamp. Compounds on the skin can reduce the light needed to kill microorganisms in the water. These compounds can damage the lamp or sleeve when they heat up. If you accidentally touch the sleeve or lamp with your bare hands, clean the area with rubbing alcohol. Allow to air dry.

4. Cover the mercury vapor lamp with the quartz sleeve. This will help to protect the lamp as well as change the wavelength of the light emitted to the best spectrum to destroy bacteria and viruses.

5. Expose the water to the light from the lamp. The amount of time the water needs to be exposed to the light depends on the amount of water being purified.

6. Wait five minutes in order to purify several gallons. Smaller amounts of water can be purified more quickly. A glass of water can be purified in about 45 seconds.

References

• Home Water Purifiers and Filters: Ultraviolet Filter
• Excel Water Technologies: UV Disinfection
• Fresh Water Systems: UV Systems and Lamps