03 Jul Let’s Go Net Zero!

Did you know it's actually possible to have buildings that are net zero on energy and water use with zero wastewater effluent? By this I mean a building site that produces as much energy as it uses and collects enough rainwater to supply all water needs plus treats, or reuses all the water we normally flush, or send down a drain. Below I describe some of the details on how this is done.

Energy – Achieving net zero energy for a home, or small-ish commercial building can be accomplished relatively easily with efficient all electric appliances and an appropriately-sized solar PV installation. This also means your water heating will usually be done by solar thermal or electric heat pump systems that don't require natural gas.

Water Supply – For a home, or office/light industrial building all the necessary water can be supplied through collecting the rain that falls on the roof. A few good rainfalls can fill tanks with a capacity of 25,000 to 30,000 gallons. For many home/small commercial sites that's a five to six month supply to get you through the roughest dry spells. Particulate filtration, activated carbon filtration and UV light treatment typically do the work of making the water fit for human consumption.

Gray Water (Wash Water) – Gray water goes down the drains of sinks, tubs, showers, washing machines and dishwashers. This kind of “waste water” typically only contains various surfactants like soaps, detergents and other personal hygiene products and is thus relatively easy to reuse. It can be used directly for landscape and garden irrigation. Some treatment is necessary, of course, for indoor reuse. Brac systems are one example of a gray water recycling system. Greywater Action provides a good overview of gray water reuse options and issues.

Black Water (Sewage) – Amazingly, our excretions we flush don't have to go through miles of pipe to energy and synthetic-chemical-intensive treatment facilities. Composting toilet systems can handle that right at your building. They break down the excrement to useful fertilizing materials, unlike septic tanks and port-a-potties. You can buy individual units like Loveable Loo, or get help designing a custom system from an organization like Lama Foundation. They also don't smell bad. My first personal experience with composting toilets was at the Hike Inn (Appalachian Trail in north Georgia) – no stench and a pleasant breeze on my behind. And, I can't mention composting toilets without recommending you watch the best promo for them ever: Poop in a Bucket.

Plenty of individual buildings have partially achieved net zero water and energy. My house, for example, is net zero energy (Green Home Tour), but no rainwater collection. Builders like Native, and developments like TerraScena also have done net zero energy with rainwater harvesting. There just doesn't appear to be much building that incorporates all the features I describe above yet. Certainly there is not much yet in Central Texas.

The concept of a net zero energy and water building is technically feasible, so why aren't we doing more of it? The logistics, legal and financing seem to be the fun and challenging bits, of course. I'm quite certain this is the way we need to go with our buildings. I'm also confident we can figure out how to make this kind of building work even in our cities. As we move toward a more sustainable future, to quote They Might Be Giants, “Zeros means so much!”