If you perform the multiple tube technique, list one advantage and one disadvant

The disadvantage of this system is that it only kills bacteria inside the unit and does not provide any residual disinfectant for bacteria that may survive or be introduced into the plumbing after the UV light unit. Maintenance requirements are minimal for UV units but the light bulb will slowly lose intensity over time and will require replacement about once a year. Some units come equipped with a UV light intensity sensor that can detect when the bulb is not emitting sufficient UV light. These sensors add to the initial cost of the unit but may pay for themselves in increased bulb life.

The advantage of this method is that it is much simpler than test tubes. The disadvantage is that it can't be used on muddy water.