Ultraviolet (UV) water treatment is used extensively by various entities worldwide, most notably by municipal water companies for drinking water and wastewater treatment, and in public and private swimming pools. Below we give some specific examples in both Ireland and worlwide.

In Ireland, UV water treatment is used by a wide array of public, commercial, and private entities, driven by both regulatory requirements and a demand for high-quality, chemical-free disinfection.

Uisce Éireann (Irish Water) incorporates UV light as a vital part of its National Disinfection Programme to ensure the continued delivery of safe drinking water and to comply with drinking water regulations. UV is used in conjunction with primary chlorination as a multi-barrier approach for robust pathogen control.
Specific examples of this include:
Leixlip Water Treatment Plant: A new UV disinfection system was installed at the "old plant" to provide secondary disinfection, a move that satisfied the Environmental Protection Agency (EPA) enough to remove the plant from a remedial action list.
Cork, Carlow, Kilkenny, and Wicklow: Irish Water has implemented UV system upgrades at numerous water treatment plants, pumping stations, and reservoirs across these counties as part of nationwide projects to standardise and improve disinfection systems.
Public and Private Swimming Pools
Many swimming pools in Ireland have adopted UV technology to improve water quality, reduce chloramine levels (which cause eye irritation and the "chlorine smell"), and enhance the overall swimming experience.
Examples include:
UCD Sport & Fitness, Dublin: Features a 50-metre Olympic swimming pool with the latest UV treatment and filtration technology, resulting in very low chlorine levels.
Kingfisher at NUIG (University of Galway): The pool water is treated by UV light, which swimmers report makes for a much more pleasant experience.
Commercial and Industrial Users
Various businesses and institutions across Ireland rely on commercial UV systems for their specific water purity needs:
Food and Beverage Industry: Widely used in breweries, distilleries, dairies, and meat/poultry processing plants to disinfect production water and comply with stringent health and safety legislation without altering the taste or odor of the product.
Healthcare and Institutional Facilities: Hospitals, nursing homes, schools, and restaurants use UV systems to guarantee high water purity for vulnerable individuals and general use.
Pharmaceutical Industry: Employs UV for critical applications like general disinfection, total organic carbon (TOC) reduction, and the destruction of ozone and chloramines in their processes.
Private Well Owners
A significant number of private individuals in Ireland with their own well water supplies are advised to install UV disinfection systems. This is a common and recommended method for treating water from private sources to eradicate bacteria (like E. coli, a concern in some Irish regions) and ensure safe drinking water at home.

Worldwide Ultra Violter is a versatile, chemical-free disinfection method used in many other industries as well.

Municipal Water Companies
Many municipal water facilities worldwide incorporate UV disinfection, often as part of a multi-barrier treatment approach, to ensure safe drinking water and meet regulatory standards, particularly for eliminating chlorine-resistant microorganisms like Cryptosporidium and Giardia.
Notable examples include:
Rotterdam Water Plant, Netherlands
A large-scale facility with a capacity of 470,000 m³/d using UV sterilization.
St. Petersburg Water Plant, Russia
Another major user, processing 860,000 m³/d with UV technology.
Orange County in California
The Groundwater Replenishment System uses UV in an advanced purification process for water reuse, producing up to 100 million gallons per day.
Singapore in Asia
Singapore: A significant portion of its reclaimed water supply (NEWater) is treated using a multi-stage process that includes UV disinfection.
Japan and European countries (e.g., Sweden, Germany): UV technology is commonly used in these regions for municipal water treatment to ensure high water quality.
Public Swimming Pools
Public swimming pools, water parks, spas, and leisure facilities widely use UV systems to disinfect water and, crucially, to reduce levels of chloramines, which are responsible for the strong "chlorine" smell, eye irritation, and skin issues. This improves the indoor climate and the swimmer experience while allowing for lower overall chlorine usage.

Examples of facilities using UV include:
H2O Herford water park in Germany.
Public swimming facilities in Sweden and Spain.
Nirvana Spa in Berkshire, UK.
Large water parks in the Czech Republic and Poland.

Other Major Users of UV Water Treatment
UV disinfection is employed across a diverse range of industries where water purity is critical.

Food and Beverage Industry: Used to disinfect water for production, ensuring product integrity and compliance with health standards without affecting taste or quality.
Pharmaceuticals and Biotechnology: Requires ultra-pure water for manufacturing processes, where UV sterilization helps maintain strict quality requirements.
Aquaculture (fish farming): Essential for maintaining clean water and preventing disease outbreaks in fish farms and aquariums.
Healthcare Facilities and Hospitals: Used to ensure high water quality in various applications within the facilities.
Residential Use: Small-scale UV systems are popular for treating well water or securing mains water in private homes, especially in North America and Europe.
Industrial Process Water: Various manufacturing and power generation plants use UV to treat cooling water or rinse water internally, promoting reuse and sustainability.