We all need clean water to survive, yet is increasingly becoming scarce on the planet. While architects and engineers have gotten much better at how to reach Net Zero Energy (NZE) with buildings, Net Zero Water (NZW) remains more of a mystery. And yet access to clean drinking water could very well define the viability of every village and city in the future. Indeed, the overriding importance of water related to the built environment has not escaped some very big governmental entities. The US Army, for instance, has taken major strides at NZW (as well as NZE and Net Zero Waste), seeing it as an imperative part of their ability to function.
There is a vital need to re-think our water supply and waste-water structures. After all, we base our supply and waste systems on technology that is over 2000 years old. And while centralized systems were extremely valuable achievements in their day, we have enough knowledge now to understand what should come next. And this is important because our cities have grown to the point where centralized systems have become less efficient than decentralized potentials. Two such examples of central inefficiencies are; first with the amount of energy it takes to pump water across urban and rural areas, and second with the problems of how to deal with massive amounts of black-water (toilet) waste- which currently is processed with toxic chemicals including chlorine. A recent study by SERA Architects found the most efficient way to handle a variety of utilities and waste is at a scale much smaller than that of cities and closer to the size of a college campus.
Thankfully there are proven ways to deal with collecting and treating water on-site. There are several barriers to such systems, such as social misperception, lack of governmental understanding, and cost- but there are several excellent examples of built projects that provide paths on how to think about these issues for the future. One such example is the Bullitt Center in Seattle, which shows that NZW and waste water treatment can be achieved, even at urban sites.
We hope to provide the basis for understanding how to conceive and design for NZW with this paper. For brevity, we will discuss a greatly simplified idea of how we think about on-site water use and provide a single-family residential project as an example. However, we will also provide links to examples of much larger projects to show that living in balance with the water cycle is achievable at essentially any scale.
MINDSET AND NZW PROCESS
Native Peoples around the world mostly lived in balance with the water cycle and their environment- though for the purpose of this paper, let's use an example of a familiar project type: A typical house. Let's imagine you are a nineteenth century "homesteader" attempting to start and run a farm on a piece of land with no centralized utility systems available. Water would likely come from one or both of two sources; A well tapping into a water table below ground; The collection of rainwater into a basin or cistern. Blackwater would most likely be treated either with an underground pit or an on-surface leach-field. If the black-water is handled correctly, the waste can be turned into fertilizer to increase crop yields. These types of systems are easier to utilize when there is enough open space for each house/project to avoid waste occurring too close to living and working spaces. However, with the use of some new technologies using ancient ideas, these processes can be placed in close proximity to populations without harmful effects. In particular, John Todd's Living Machines have been in use for decades with great results.
To demonstrate how to conceive of getting in balance, and possibly "off the grid" when it comes to water, let's look at a simple residential example to understand how to consider and design for NZW. Look at the example graph and you'll see the tall column on the left representing typical water usage for a family of 3-4 people living in a single family home with a small yard including a patch of turf lawn (column A). What you'll notice is how much certain uses consume. The initial process to getting in balance is to reduce water usage as much as possible before considering the options for water collection.
By eliminating the turf, utilizing xeriscaping (native drought-tolerant plants), installing low-water use fixtures (such as low-flow sink faucets and dual-flush toilets), and good individual practice (the 4-minute shower, for instance), much of the water load is reduced as shown in the second column (B). This means we need to collect less water to achieve balance, which is a huge help. There are even some new low-flow shower heads that actually work well. Most low-use fixtures have been shown to lower actual water use. And though we all enjoy having turf and lush landscaping, we can instead consider increased placement of neighborhood parks, which can utilize area storm-water re-use to supply landscaped environments for entire neighborhoods. These communal spaces may also form better social cohesion and reduce social isolation. And there is an alternative to conventional turf, which is UC Verde Buffalo Grass, which uses only 20% of the water of turf and never needs mowing. Ok, let's return to our graph example...
In column C, you can see that we've eliminated the need for landscaping irrigation with careful plant choices. We've also eliminated the need for water used for toilets by replacing them with composting toilets. While such toilets conjure up negative visions of port-a-johns or smelly camping facilities, new technologies in composting toilets with vacuum flushing (similar to what you've likely used on airplanes) provide bathrooms without odor and improved health over conventional toilets that spray germs with every flush. There is a choice here, though. One could choose to keep traditional water-flush toilets, but this comes with the requirement to collect more water and treat a greater amount of black-water. So, for this exercise, to keep it simple, let's stay with the example of composting toilets.
For the use of composting toilets, there are now "plug-and-play" appliances that collect and treat the waste with non-toxic bacteria. The end result is a compost that may be utilized in gardens or sold (helping to recoup costs of the equipment) to companies that resell the waste as commercial fertilizer. If one chooses to additionally utilize a urine diverter in the system, the liquid waste may also be sold to companies for fertilizer and even for processing the resulting metals.
Now that we've reduced as much as we can on the water requirement side, we know how much water we need to collect. Let's assume that our residential example is a 1500 SF house in the Phoenix Metropolitan area (PHX)- a place with far less annual rainfall than much of the USA. Even in the Sonoran Desert we can collect 6000 gal/yr from a 1500 SF roof area. The majority of the rainfall in PHX occurs in July & August during the monsoon period, with almost all the remainder falling in January & February. This results in long dry seasons between the two wet seasons. In order to stretch out the collected water through the dry periods, we have to gather everything possible during wet months and store the water. This requires large containers to be installed, monitored, and maintained to eliminate algae or other harmful agents. In column D, you'll see how far the rainwater collection and reuse gets us, with our water requirement now dropped to just 8,000 gal/yr.
The other methods of water collection come through greywater (non-toilet uses such as laundry and showers) and black-water (toilets). As we've decided to use composting toilets in our example, we will skip the latter for this paper. Greywater also needs to be stored, but since it is collected on a daily basis (rather than seasonal), we don't need to add much additional water containment space. However, this water needs to be treated a bit more with enzymes and bacteria to ensure the water creates safe reuse for showers, laundry, and dishwashing. Here again, plug-and-play products are available, including for residential projects. By reusing this water along with rainwater and the reductions in usage, you can see in column E that we have achieved NZW.
This examples shows a pathway to living in balance within our imaginary site, but let's take a moment to discuss some real-world barriers we likely have in our way. One perceived barrier is a lack of space for a given project. But as discussed earlier, urban projects such as the Bullitt center have shown that it need not be an insurmountable problem. It may add cost for the extra equipment required to achieve balance, however. And cost for the equipment, extra piping, and water storage systems may definitely be a barrier. But even if cost isn't a problem, quite often governmental regulations are in the way of gaining approval for the use of these systems. In Maricopa County, for instance, there is a requirement for all projects that have access to centralized water and waste systems MUST be connected to them. And many health regulators do not approve of on-site water collection and reuse. It can take a great deal of convincing to get regulators onboard with a project's goals. It may even require a client to become their own registered 'utility supply company'- though that may not be as difficult as it sounds. Still, the barriers are real and it takes a good deal of patience from designers and project owners to clear the hurdles. It also wouldn’t hurt if there was a greater amount of advocacy to demonstrate working project examples to regulators.
And while the path to living in balance with the water cycle may not be initially easy, there are huge benefits to our cities and planet. The good news is that there are some very good examples of projects out there finding new ways to achieve real NZW and potentially even creating a new interconnected infrastructure for collected and treated water. By sharing water across projects, we can help raise the efficiency of decentralized water production and usage.
Our planet is struggling to provide clean water sources as the population and industrialized production increases. Extended droughts are also creating dry areas with large populations, and many reservoirs and lakes are at record low levels. We have never lived in a time where producing projects that exist in balance with the water cycle has ever been so important. The project value of producing NZW projects is increasing, and it is important as owners, clients, designers, and students to understand the fundamentals of designing and living responsibly when it comes to water. We hope this paper will provide a basis for greater change when it comes to how we deal with on-site water, even in extremely dry areas such as Metropolitan Phoenix.
For more information on water issues, NZW design and barriers, see this excellent report.