How to Detect Bacteria in Water With a Black Light

Make a note of any appliances in your kitchen that use water. A common appliance in your kitchen that may use water is your refrigerator if it has an ice maker or a water dispenser.

Turn off all of the lights in the room. Close all curtains and window shades to make the room as dark as possible. You can also wait until the sun goes down and it's dark outside.

Press the “Power” button to turn on your portable black light. Perform a scan of the room by starting in one corner of the wall and working your way around the room.

Go from wall to wall and shine the black light from the floor up to the ceiling. Concentrate in areas that are hard for you to see, such as along the baseboard. These are areas where water can penetrate and hide bacteria.

Shine the black light over each every item in the room. Scan the light over the countertops, in the sinks and around the bathtub. Make a note of any areas that illuminate when exposed to the black light.