Rainwater Collection
To achieve net zero water, we need to first determine the volume of water we are able to capture from our roof area and store, and then how much of that can be used for each application necessary for us to sustain our site. Determining how much rainfall you can capture depends upon how large a roof area you have and how accessible that surface is in terms of installing a gutter, downspout and piping system to carry your capture to storage tanks. The storage capacity you will need is determined by looking at the rainfall patterns for your area and assessing the size of containers needed to manage enough water to meet your family’s needs over time. This is usually calculated on an annual basis, considering that we may get our rain seasonally yet need to store enough water to meet our need during the non-rainy periods of the year. As an example, Austin, Texas, and Portland, Oregon, get about the same amount of annual rainfall, but Portland gets theirs in frequent mild showers, while Austin’s comes in a few severe flashflood events with little rain in between. Austin families must have more storage capacity to be able to last longer between replenishing rain events.
Approximately 600 gallons of water can be collected for every 1,000 square feet of collection area, or 0.6 gallons for every square foot of roof area during a one-inch rainstorm. Based on your available roof collection area and the configuration of your gutter system to capture and collect roof runoff, you can determine how many gallons of rain you can expect to collect from each one-inch rainfall. Next you will need to calculate how many gallons your family uses on a daily basis and then think about how long the average period is between measurable rainfall events in the various seasons where you live. This will help you determine how much storage capacity you will need. Of course, the higher your water needs, the larger the collection area and storage container you will need.
You’ll need to store enough supply to meet your daily needs in your lowest rainfall season until the next rain, unless you plan to purchase water to keep your tanks replenished. Purchasing water this way (one truckload at a time) can be expensive and adds significant embodied energy, and it doesn’t really meet our goal of net zero water, so it should only be done in periods of unexpected prolonged drought. Also, depending on the water source, it probably is not going to be the same quality of water that you will get from pure rainwater.
As mentioned earlier in this article, it is necessary to keep separate storage units to meet your different needs. Just as it is a waste of energy for water utilities to treat supplies for irrigation, it is also a waste of resources for you to use your filters for treating rainwater for potable use for water you will use in your landscape. You should separate your calculations for each end use to determine the volume of storage you will need for each and the various piping configurations to get the water to where it will be treated for use or used without treatment, as necessary.
For indoor potable water, you must install a filtration system and complete disinfection by using ultraviolet light or ozone treatment. For our own health and to protect the environment, the treatment method should be able to provide safe water without the use of chemical treatment. For non-potable water use, if you can reduce your needs to a minimum, it would not be cost-effective to separate storage.
Water Reuse
Water reuse may be the last frontier of water conservation strategies. It requires dual plumbing of the home both for separating potable and non-potable delivery and for separating graywater and blackwater discharge. Beyond those secondary uses or treatments, even more additional plumbing is required for different tertiary applications.
Graywater
The initial stage of this initiative is graywater reuse. Acceptable graywater sources may vary according to local jurisdictions, but generally accepted sources are lavatory faucets, showers and tubs and the clothes washer wastewater. Some authorities also allow kitchen sink wastewater (except that from garbage disposals), and others prohibit water from bathing activities. You should check with your local regulatory agencies before plumbing for this type of system.
In some cases, graywater has been plumbed from bathroom lavatory sinks to be used again to flush toilets. It can also be carried directly out into the landscape by plumbing that discharges it separately from the blackwater discharge lines from kitchen sinks, dishwashers and toilets that go into wastewater treatment. However much graywater is sent to the landscape may not be enough to reach desired root zone depth, possibly even encouraging shallow root development that exasperates water stress, so it may only represent part of the equation for meeting our outdoor landscape water needs. But as we move away from dedicating water for landscape use, it may be sufficient for what remains. There may be regulations that limit the holding period for graywater storage, so, again, check with local regulators before designing your reuse system.
Studies can provide us with research as to the typical amount of water available from these sources, based on family size and lifestyle patterns. You should make adjustments to any published calculations if your family’s activities include showering at a gym or children leaving for boarding school for months at a time. It is also important to note the age of any study research references. As faucets and washing machines get more efficient at using water, the amount left to contribute to our graywater supply may be greatly diminished from published averages. This is especially true of newer clothes washers that only use four gallons per cycle and motion-sensor predetermined-flow lavatory fixtures, which should be on your want list to reduce overall water needs.
Condensate
The reuse category also introduces new sources of water for available use. In regions of the nation with high humidity and scorching summer temperatures, collecting condensate from air conditioners can yield substantial supplies of non-potable water. Additionally, condensate can supplement untreated rainwater for outdoor use during extended drought periods, when rainwater stores might otherwise be exhausted. In green mixed-use developments, condensate is available not only from our own residential air conditioning systems, but also from the excess generated by commercial systems, especially those on large office buildings, hospitals and industry located within the same development. The same is true of chilled water from large commercial chillers, which can be distributed both as a means of providing radiant cooling and as an irrigation water source.
Just like other forms of gray water, condensate from air conditioning systems can be combined with untreated rainwater, used, then reused as graywater or treated for reuse. Although condensate quality is about equal to distilled water, exposure to contaminants in systems and storage containers does not allow for its use as potable water. However, it serves well as a supplement to irrigation water, as well as for clothes washing and flushing toilets inside the home.
Care must be taken when reusing water from many commercial HVAC chillers (different than condensate) since it is often treated with chemicals to prevent corrosion or scaling that could be toxic. This requires community infrastructure to support piping it to the locations where it can be used. It also may encompass various types of water treatments, recapture methods for repeated reuse and storage facility management. Just as our solid waste is now being viewed as a recyclable resource, we need to recognize that what was once considered wastewater is merely water that requires additional treatment for reuse.
Stormwater Runoff
Capturing stormwater runoff on the site can provide another source of irrigation water; it might even be used for some indoor non-potable water applications. The goal is to manage water on our own site using the most energy-efficient methods possible, especially if we also have a net zero energy goal. Remember our basic principle from this article: water runs downhill. We will use much less energy moving water from our rainwater cisterns to our point of use if that direction is downhill. The same goes for removing wastewater after use: plumbing should flow downhill to the reuse or treatment system. Keeping this downward flow going as much as possible through all of our processes means using the least amount of energy for those processes.
For landscape use, water can be diverted through a series of berms and swales or use an underground French drain system. This water is directed to landscape beds or stored in retention ponds and pumped out as needed for various uses. Other permanent erosion control features can also help to manage and keep water on the site.
Permaculture methods can capture runoff on the high side of trees, allowing it to infiltrate at these points, feeding water down to the tree roots by natural flow and subsurface distribution. This technique encourages the use of materials available onsite, which can include brush, mulch or downed tree trunks and branches, to slow water down as it moves through its natural course downhill. In landscapes with a significant slope, retaining walls should be built to terrace the area, reducing erosion of native soils and runoff and improving infiltration. The more we can use these types of features to keep natural rainfall on the site, especially soaking in to promote deep root growth, the less supplemental irrigation we need to provide. In this way, literally all the rain that falls on your site that does not infiltrate immediately into the soil can still be used.
Onsite Treatment
We need to develop onsite methods to treat water to varying degrees, based on the level of water quality needed for each different use. This includes the ability to treat “water waste” onsite for use again and again, if possible, in a closed-loop system. We must also treat any wastewater to be discharged from the site so as not to cause damage to our soils, neighboring groundwater resources or ecosystems.
If you have a large household that generates a large graywater volume, beyond your ornamental landscape needs, you should consider onsite treatment that would purify the water for edible food crop use. Biofilters can remove many organic substances that contaminate water during bathing and clothes washing. Of course, the use of biodegradable cleaning products is necessary to prevent chemical contamination that cannot be treated onsite. At a single household or on a community scale, constructed wetlands are able to process and return graywater to a usable state for a very low cost, removing pathogens, bacteria and non-biodegradable toxins. And the beauty of this system (other than the fact that it can be a beautiful addition to the landscape) is that it can treat the same water repeatedly for reuse.
Of course, various types of septic systems can be used to treat and manage blackwater and fecal waste, but those are dead-end systems. Composting toilets, however, provide the benefit of not requiring water to flush waste through like conventional sewage piping does. Some models are now available with urine separation, which provides composting opportunities for human feces without the need for blackwater treatment at all. Urine is a wonderful fertilizer that may be utilized right away because it is inherently sterile. Human waste can be processed as manure for uses other than food production. Care must be taken whenever using human feces to ensure that it is thoroughly composted and raised to the necessary temperature to make it safe to handle.
Other Water Resources
As we indicated at the start of this chapter, water independence means that we can fulfill all of our site needs using water that we can capture and reuse, such as rainwater and condensate. Only three percent of the world’s water is freshwater, the majority of which is ice. Less than one percent is readily available for use by humans. So many are considering and investigating desalinization of the vast supplies of water in the world’s oceans.
In this article, we will look at the issues contributing to and caused by carbon emissions on our planet. One of those that we will mention relates to the amount of carbon that is sequestered in those vast ocean areas. The ocean stores approximately one-third of the carbon sequestered on Earth each year, but as carbon emissions grow, this is causing ocean acidification, threatening this essential ecosystem. The rise in ocean acidity is leading to the global demise of coral reef systems due to a lack of calcium carbonate to construct and sustain their structure. Coupled with overfishing and increased pollution activities, as well as warming of ocean temperatures, fish populations worldwide, a major source of food for many cultures, are in decline. Many are already facing possible extinction.
Many desalinization methods dispose of the removed salt, or brine, in ways that can cause significant contamination to our soils, groundwater and surface water supplies, or further damage our oceans. Treating one water source to contaminate another (or others!) just makes no sense at all. Coupled with the tremendous amounts of energy and infrastructure needed to manage the treatment and distribution processes, and the greenhouse gas emissions resulting from the operations, the result is not unlike the unsustainable water systems we already have in place.
Case Studies
There are plenty of studies available on the numerous examples of people who are, for one reason or another, living off the water grid. These range from areas without municipal water connections and unreliable groundwater supplies to those living in remote locations, like mountainous areas where rainwater catchment is a less expensive investment than drilling a well for groundwater. It’s not a matter of whether or not this is something that we can accomplish, it’s a matter of when it will become mainstream.
Although there has been research into applications of the strategies discussed in this chapter, we are not aware of any particular instances that incorporate them into a net zero water scenario that fits our model. So, we’ve created a vision of a closed-loop system that would accomplish this goal.
- Roof designed to capture sufficient rainwater: storage capacity based on annual precipitation and indoor potable water need of family with backup capacity for fire protection or in case of extended drought, would supplement water needs for food production
- Site built to capture and use the residual stormwater
- Graywater system installed to reuse water from laundry, lavatories and showers; discharged to biofilter pond
- Edible landscape installed in wicking gardens built using expanded shale and compost, with a good mulch layer maintained
- Fruit and nut tree soil amended with expanded shale and compost, with a good mulch layer maintained
- Remaining landscape is wildscape (natural habitat restoration), reusing native soil amended with compost
- Composting toilets installed so no human waste enters wastewater system
- Blackwater from kitchen sink directed to biofilter
- Permaculture techniques used in landscape to direct water to retaining ponds
- Condensate lines discharge HVAC water into a specialized storage tank containing water from the biofilter
- All indoor potable water supplied by rainwater filtration system
- All laundry water and garden water sourced from biofilter/condensate storage tank
- Stormwater retention pond(s) used to irrigate edible landscape garden and trees
Again, make sure any of the strategies you choose for your project are allowed by local and state laws. If nothing else, many of these can be incorporated into your outdoor landscape water management plan. Permaculture techniques have long been used to manage stormwater runoff as a source of landscape irrigation. Improved gardening methods can significantly reduce the amount of water needed. These are steps in the right direction that we can all benefit from.
