You’ve probably heard the term Net Zero Energy before, but have you ever heard the term Net Zero Water? This up-and-coming concept is considered one of the most stringent goals laid out in the Living Building Challenge (LBC). Sure, the LBC requires a building to abide by Net Zero Energy rules, follow a strict materials list, have all goods and services produced locally, recycle all construction waste, maintain excellent indoor air quality, and more. However, probably the most abstract prerequisite of this challenge to us is the water independence aspect.
In order to achieve water independence, a building must capture all precipitation, manage all storm water runoff, and re-use all household wastewater. ”Wastewater” can either be considered greywater or blackwater, depending on the source and contact with organic matter. Greywater is not riddled with pathogens, but is still not clean enough to be used for potable (drinking) purposes. Greywater comes from places like the laundry machine, the bathroom sink, showers, and baths. Blackwater has come into direct contact with organic matter and/or human waste. Blackwater sources include the garbage disposal, toilets, and sometimes dishwashers.
It may sound a little disturbing at first, but you won’t be drinking your treated toilet waste or anything, that serves better to be treated and re-used to irrigate, flush toilets, or to cool HVAC systems. Different types of water require different types of treatment. For instance, rainwater can be captured, stored, and treated with a relatively insignificant amount of energy. This is because rainwater is fairly clean – it just requires ultra-violet sterilization to be used for drinking purposes.
Greywater can be naturally filtered in a constructed wetlands system, or a “Living Machine.” In order to treat this water, you simply let gravity carry it through each chamber in the Living Machine, where plants and animals naturally clean it as they would in nature. Here’s a diagram from a past project of mine showing how this system works:
Although there have been attempts (2, 3) at achieving the LBC standard, so far none have completed the task. Net Zero Water is an idea we’ve been kicking around at Postgreen, and it seems to be the main hurdle we’ll need to leap before achieving the stringent standard.
I’ve put a site up pertaining to net zero water, which aims to compile some of my thoughts and research on the topic, as well as provide a place for discussion and the sharing of information. Please check out NetZeroWater.com and feel free to subscribe to it for updates!