“I told them that they were nuts to be considering slow-sand filtration when the technologies are out there such as membrane filtration”, he said. I held my tongue.
While there are cases where the use of membrane filtration are warranted, the level of reliance on technology in this instance is akin to using an autoclave to rinse out your coffee mug, believing that the protection is warranted, regardless of the cost. The water quality in question hardly requires filtration to achieve compliance with health objectives, and the existing slow sand system is relatively simple.
I am by far the last person to speak out against technology on the whole, but I do believe that there are appropriate levels for different applications, and stating that the most current technology is necessary just because it is the latest is poor decision making. Other factors that I see as necessary include installation, operating, maintenance, and staffing costs over the lifecycle of the plant. Also important are factors well outside of the control of the utility operators such as power costs, and the cost and/or availability of membranes or other replacement parts in the future. Membrane filtration is wonderful and is a technology that has the ability to clean water that would otherwise not be potable.
For long term infrastructure such as a water system, it is necessary to think outside of the stable economic scenarios we believe we live in today. Simple risk management says that in the event of a component failure occurring at a time of strife, (whether financial, political, transportation, or natural disaster), the ability to continue to provide clean water would be compromised. We don’t build these systems just for the “good” times.