Once completed all samples are sent to the testing laboratory and examined under lab conditions. Regular reviews and monitoring of the water supply is recommended to determine if any changes have occurred. Typically, a Legionella risk assessment should be conducted every 2 years unless something changes in the water system.
When was the last time an inspection of the water supply/system was conducted? If never, then it would be wise to check that your water storage system is not habouring any bacteria that could cause a health risk!