UV Water Purification: How It Works and When You Need It

Ultraviolet (UV) water purification is one of the most effective and underutilized water treatment technologies available for residential use. It kills 99.99% of bacteria, viruses, and protozoa — including E. coli, Giardia, Cryptosporidium, and Legionella — without adding any chemicals to your water.

For Central Ohio well water homeowners, UV sterilization is often the missing piece in an otherwise complete treatment system.

UV sterilization uses ultraviolet light at a specific wavelength (254 nanometers) to damage the DNA of microorganisms. When a microorganism's DNA is damaged by UV light, it can no longer reproduce — it's effectively neutralized even if it's not immediately "killed."

The process is purely physical — no chemicals are added, no byproducts are created, and the water's taste, odor, and chemistry are completely unchanged.

UV dose: The effectiveness of UV treatment is measured in mJ/cm² (millijoules per square centimeter). The NSF/ANSI 55 standard for residential UV systems requires a minimum dose of 40 mJ/cm² — sufficient to achieve 99.99% (4-log) reduction of bacteria and viruses.

• Bacteria: E. coli, coliform, Salmonella, Legionella, and thousands of other species
• Viruses: Norovirus, Hepatitis A, Rotavirus, and others
• Protozoa: Giardia, Cryptosporidium (which is resistant to chlorine but vulnerable to UV)

• Hardness minerals (calcium, magnesium)
• Iron or manganese
• Nitrates
• Heavy metals (lead, arsenic)
• Chemical contaminants (PFAS, VOCs, pesticides)
• Sediment or turbidity

UV is a disinfection technology, not a filtration technology. It's one component of a complete treatment system — not a standalone solution.

This is the primary application for residential UV systems. Private wells are not regulated or treated by any government agency. Bacteria can enter a well through:

• Flooding or surface water intrusion
• Cracked or deteriorating well casing
• Improperly sealed well cap
• Nearby septic system failure
• Agricultural runoff

For Central Ohio well water, we recommend UV sterilization as a standard component of any complete treatment system — even if your current water test shows no bacteria. Well water quality can change, and UV provides continuous protection.

Homes drawing water from ponds, streams, or rainwater collection systems should always use UV treatment. Surface water has high biological contamination risk.

If your well has been flooded, UV treatment should be installed after shock chlorination to provide ongoing protection.

For households with members who have compromised immune systems (cancer patients, transplant recipients, HIV/AIDS, elderly), UV treatment provides an additional layer of protection even on city water.

UV systems are sized by flow rate — gallons per minute (GPM). The system must provide adequate UV dose at your home's maximum flow rate.

Sizing guide:

• 1–2 bathrooms, 1–3 people: 5–8 GPM system
• 2–3 bathrooms, 3–5 people: 8–12 GPM system
• 3+ bathrooms, 5+ people: 12–15 GPM system

Important: UV effectiveness drops dramatically if the water is turbid (cloudy) or has high iron content. UV light can't penetrate particles — bacteria can "hide" behind sediment. This is why UV systems must always be installed downstream of a sediment filter and iron filter.

For UV to work effectively, the water entering the UV chamber must meet these standards:

• Turbidity: less than 1 NTU
• Iron: less than 0.3 mg/L
• Manganese: less than 0.05 mg/L
• Hardness: less than 7 gpg (higher hardness can cause UV sleeve fouling)
• Color: less than 15 color units

For Central Ohio well water with iron and hardness, the typical treatment sequence is:

Sediment pre-filter → Iron filter → Water softener → UV sterilizer

The UV system goes last — after all the other treatment stages have removed the particles and minerals that would interfere with UV effectiveness.

UV systems require minimal maintenance but it's critical:

UV lamps degrade over time — they lose intensity even if they still appear to be glowing. Most residential UV lamps are rated for 9,000 hours (approximately one year of continuous operation). Replace the lamp annually, even if it still appears to be working.

Never skip lamp replacement. A degraded lamp may appear functional but provide insufficient UV dose to kill pathogens.

The UV lamp is enclosed in a quartz sleeve that protects it from the water. Minerals and iron can deposit on the sleeve, reducing UV transmission. Clean the sleeve with a soft cloth and diluted acid (citric acid or white vinegar) when you replace the lamp.

Check the O-rings, end caps, and chamber for any signs of leaking or corrosion. Inspect the controller for error codes.

Some homeowners use chemical chlorination (chlorine injection) as an alternative to UV for bacteria treatment. Here's how they compare:

For most residential well water applications, UV is the preferred choice — it's simpler, requires no chemicals, and doesn't affect water taste.

Pure Aqua Columbus installs UV systems as part of complete well water treatment packages throughout Franklin, Delaware, Licking, and Fairfield counties. We size the system to your home's flow rate and configure the pre-treatment sequence to ensure UV effectiveness.

Learn about our well water treatment systems → | Schedule a free water test →