At the time of a DNA Multiscan of untreated water an Aerobic Bacteria test be should done on a plate . This will give you a good visual of the quantity of bacteria that are growing. After the initial DNA scan Agrozone recommends doing plating on a weekly basis to make sure that pathogens are being kept under control by the disinfecting method.
Most bacteria are not important as a pathogen for most greenhouse water supplies but are important to keep below 10000 cfu/ml to prevent biofilm
With some training most growers can do this themselves or you can send the samples to a Lab.
Agrozone has been working with AWLS for on farm water collection and plating for quick results.