When looking at our annual utility bills I have trouble visualizing how much electricity we are using. In 2010 we used 12,275 kWh of power to function in our home (not including the gas for the kitchen stove). This was for ~2.33 full time adults (house guest for part of the year) and 0.17 baby in about 2200 SF. Coal burns at roughly 2460 kWh/ton (accounting for efficiency loss). If we assume that Dominion Power runs on 100% coal (although it may be close to 50% nuclear or hydro), we used almost 5 tons of coal to bath in hot water, watch movies and have a machine wash our clothes and dishes! That sounds like a lot. I’m starting to feel a bit sad.
When I look at our water use in 2010, it is 72,098 gallons. This also included two additional adults, as our back studio apartment is on the same water supply. This quantity of gallons may also be hard to imagine. But picture a 20′ x 40 ‘ x 5’ swimming pool (4,000 gallons). That is 18 swimming pools worth of water!! For what? Bathing, drinking, washing dishes and watering plants for just one year? Wow. Oh wait, I forgot something. Toilet flushing. Toilets can account for as much as 27% of household water use. In case you forgot, that water is 100% potable water that our taxes have paid the City to clean. Unless our dog Felipe is picky, this level of cleanliness is not necessary in our toilets, and in my mind a waste.
So how can we break down this usage? Water that leaves the house as “sewage” can actually be broken down into two types of water:
1) Black Water: Wastewater contaminated by feces or urine, which includes water used in the toilet, urinal or bidet.
2) Grey Water: All remaining water coming from the shower, bath tub, and hand sinks. Water draining from kitchen sinks, dishwashers and laundry (cloth diapers) are also generally considered grey water, although if left to sit for 24 hours, can quickly become more like black water as the oxygen eats up the food, soap and oil bacteria and it becomes anaerobic.
But how about that shower, tub and sink water? Couldn’t it be used in the toilets, doubling the life of the grey water and almost eliminating the amount of potable water needed for flushing? Yes! We found a system that does this. The Water Legacy-55 keeps all of the grey water in the plumbing system and exits out to the City sewer once it becomes “black.”
What is the payback of this $3200 unit? If we take 3 showers /day @ 4 minutes @ 2.0 gallons/minute (low-flow head), then we are using 24 gallons a day. If we (3) each flush the toilet 5x/day @ 1.28 gallon/flush (low-flow toilet), then we need 19.2 gallons in toilet water a day, or 7008 gallons/year. That looks about right. City of Charlottsville water costs roughly $0.014/gallon, so we could save $0.27/day or $98.55/year. Ignoring inflation, it would take about 32 years for this system to be paid off just on the savings from not using potable water for toilet flushing. A tough sell. However, this is partly because we install Water Sense extra low-flow toilets. New toilets use 1.6 gpf, although many houses still have older 5 gpf toilets. Further, City water is very cheap. (Compare $0.014 for one gallon of City water and sewer to $1.50 for one liter of bottled water.) I’m curious to see if the price goes up with the new dam, and on Monday the City will likely announce a 28% price increase.
While we are talking about it, City potable water is also not necessary for watering all the plants in the garden either. As for using potable water for irrigation, I don’t think it makes sense to use grey water in the yard. Even if we try to use environmentally benign soaps and household cleaners, I don’t know enough about chemistry to understand how human products can effect our plants, much less our public watershed. That being said, I do know that rain is a pretty good substitute for potable water on plants. I love that the City water comes out of the hose at a nice high pressure and that I can drink it, but can these traits be recreated? Having used rain barrels in the past, I know that they can fill up very quickly in a rain storm. Having proper civil engineering to get the water overrun functioning is key. If we want to harvest rain for landscaping, I am starting to think about getting a larger cistern that would be underground with a pump. This seems a bit excessive, but could be worth it. Let’s see…if we use the hose for 10 minutes / day @ 3 gpm = 30 gallons/day. Let’s say 3 days / week for 3 months…270 gallons. That is not actually very much. Perhaps I am being conservative, but at $455 for a 325 gallon cistern, the payoff at $0.014/gallon would be 120 years.
As for buying the grey water system and the rain cistern, I think the money we are spending on the WaterSense low-flow shower heads and toilets and new efficient dishwasher and washing machine is better spent. I haven’t quite done the math to pull out the added cost for these, but it cannot be more than a few hundred dollars and should drop our usage down some thousands of gallons/year for years to come. I’ll work on that math…