Feature: Water conservation during floods

It is interesting the way the human mind stores memory. I am quite convinced that humans have a relatively inaccurate sense of the past, both short- and long-term. One week this summer, it rained for four straight days, then there was a sunny day, and on the sixth day … it rained again. What are the words I heard from people as I complained that yet another one of my croquet games was being canceled?

“Well, we need the rain.” It was the same during the drought. After a couple days of drizzling rain, people would be saying, “What drought? It’s rained a lot this year.”

In the world of green building, we pride ourselves on long-term thinking. So after three consecutive years of drought, I decided it was finally time to invest in a 650-gallon rainwater catchment system for irrigation. Yet in the summer of 2009, the tomatoes in my garden were more likely to get some fungus from being too wet than needing to be watered. I certainly don’t regret my choice to put in the system, but I wanted to help others understand why — as the French Broad River overflows — I still push just as hard for low-flow showerheads and rainwater catchment.

Some people reading this have the pleasure of knowing the water that flows from their faucet comes from a clean well no more than 100 yards from their home. For the majority of us, on the other hand, our water is impressively supplied via miles of infrastructure and a complex process of treatment to guarantee it is safe to drink, with the source being some reservoir who-knows-where. Without understanding what happens behind the scenes, it is often hard to appreciate what it takes — besides the 21 million gallons of water that the Asheville Water Resources Department typically delivers each day from its two reservoirs (North Fork and Bee Tree) and the Mills River — to supply that nice hot shower we tend to take for granted.

The process goes like this:

From the reservoirs or river, the water is pre-chlorinated and mixed with aluminum sulfate to coagulate suspended particles coming from the lake. After mixing, the water flows through the filters, which remove coagulated particles. Following filtration, the pH level is adjusted, fluoride is added for dental health purposes, corrosion-inhibitors zinc orthophosphate and sodium bicarbonate are added (to reduce the potential of lead entering water in older home plumbing systems), and the water is once again chlorinated for further disinfection. After treatment, the water travels through a portion of more than 1,643 miles of water lines and is stored in one of 33 storage tanks located throughout the distribution system. In order for the water to have enough pressure to more than dribble out of the faucets, it must go through one of 35 booster pump stations that increase the pressure in the lines.

According to data supplied by Maggie Ullman, energy coordinator for the city of Asheville’s Sustainability Office, the process requires one kilowatt hour for every 570 gallons of water supplied by Asheville Water Resources. The average person uses about 60 to 80 gallons of water a day at home. Average water usage throughout the Asheville Water Resources area is about 170 gallons per person, per day (including business and industry use).

After being used, most of this water flows down the drain toward its eventual arrival in the French Broad River — but not before it’s treated at the Metropolitan Sewerage District’s French Broad River Water Reclamation Facility.

Gravity, or sometimes pumps, sends the wastewater through a portion of the near 1,000 miles of sewer lines that comprise MSD’s collection system. At the treatment plant, the wastewater first travels through bar screens that remove debris and solid waste, which is sent to the county landfill. The wastewater is then pumped to a process designed to remove grit and inorganic solids, which is sent to the county landfill as well.

The wastewater then goes through a series of rotating biological contractors, which is the true heart of the treatment process. After the RBCs, the wastewater is pumped to a clarification or settling tank to remove solids; these “biosolids” are then de-watered and incinerated onsite. In the final steps of the treatment process, the reclaimed water is disinfected via chlorination and then de-chlorinated before it is returned to the French Broad River.

According to MSD Director of Administration Peter Weed, the cost per million gallons of wastewater treated is $175 or 1,750 kwH.

So after all that work to get water to our homes and businesses and then treat what we put down the drain, it only makes sense to use every drop as efficiently as possible and minimize our impact. It is important to think about resource use in a holistic way — recognizing that everything consumed takes many other resources in its production and disposal. Just as it’s been illustrated here that water conservation is in fact energy conservation too, energy conservation reduces water use.

[Matt Siegel is director of the WNC Green Building Council. He can be reached at matt@wncgbc.org or at (828) 254-1995.]