Office water testing provides evidence about selected microbiological, chemical and physical characteristics for a defined purpose. Drinking-water investigations, Legionella analysis and operational checks answer different questions. HSE says workers must have access to drinking water and relevant water-system risks must be managed. Landlords, managing agents and occupiers need clear responsibilities for shared systems, tenant equipment, records and responses. Testing can investigate complaints, suspected contamination, plumbing-related concerns or verification following relevant work. Incoming supply quality and conditions inside a building are separate considerations. HSE explains that microbiological monitoring is not usually required for generally enclosed hot and cold water systems, though testing may be necessary where control effectiveness is uncertain or recommended conditions are not achieved. An office with evaporative cooling equipment needs a different programme. Legionella sampling does not replace risk assessment, maintenance or operational controls. Drinking-water indicator tests differ from Legionella analysis. DWI explains that lead can enter water from plumbing and fittings, with standing time affecting concentrations. Dispensers and filters need equipment-specific hygiene and maintenance. Hybrid working, low-use outlets and closures can require review of control arrangements. Samples need precise locations, appropriate first-draw or post-flush methods, suitable containers and method-specific transport. UKAS accreditation applies to specified tests and sample types. Reports need correct identities, units, methods and interpretation criteria. Not detected is not absolute absence, and one satisfactory sample is not a permanent guarantee for a whole office. Significant findings require documented investigation and proportionate action. Testing frequency should be justified for the actual premises. Reviewed 7 October 2026 using HSE, DWI and UKAS guidance.