UV disinfection
Clear-looking water can still carry Cryptosporidium and other microbes that chlorine alone does not always stop.
What it is
Ultraviolet light inactivates microbes in a drinking-water plant without leaving a chemical residual. Validated reactors are standard practice under the U.S. EPA Long Term 2 guidance. This is a plant barrier for drinking water, not a desalination membrane and not a wetland filter. Singapore’s NEWater uses ultraviolet light as one step in municipal wastewater reclaim; that is a different practice.
How it works
Water passes a bank of ultraviolet lamps inside a reactor. The dose has to be validated for the flow and the clarity of the water. Turbid water and unvalidated lamps fail. Ultraviolet light does not leave a residual in the pipes downstream, and it does not remove salts or most chemicals.
Where it already runs
The U.S. EPA Ultraviolet Disinfection Guidance Manual and the Long Term 2 rule documents are the reference for validated reactors. The photograph is the Sooke River Road ultraviolet disinfection plant in British Columbia, a municipal drinking-water works.
Limits: what it does not fix
No lasting residual in the distribution network. Turbid water and unvalidated lamps fail. Ultraviolet disinfection does not remove salts or most chemicals.
Sources
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