Greywater practicalities: Receiving

To finish up our introduction to greywater, we’ll cover the receiving system. This is my favorite part of the system. We get to think about gardens and trees!

Greywater should not be used to water above the surface (leaves, grass, etc.) nor should it be used to water food. Greywater should be used to apply below-surface watering to non-food plants. Food producing trees are an exception to the “don’t water food rule” as long as the water is applied only to the roots.

Non-pressurized distribution systems are generally well suited for sending a fairly large amount of water to a fairly small number of end points. This makes trees great candidates for greywater receivers. Trees need large amounts of water, and they can handle getting significant doses at one time.

To be most effective, trees receiving greywater should be planted in mulch basins (actually, mulch basins are generally a good idea for trees). Mulch basins allow water to be purified much more effectively than a tree just planted in the ground. A mulch basin starts with a basin with an island in the middle. The tree is planted on the island so that it does not sit in the water. The basin is filled with mulch which both prevents the greywater from being exposed to the surface and slows the flow of water, allowing better infiltration into the soil.

When greywater transitions from the distribution system to the receiving site, it should either flow into an underground chamber or directly into a mulch basin which can quickly prevent it from being above ground. This part of the system must be designed to avoid clogs, both from the greywater itself and from the material that the water is being let into (or slugs, as apparently they sometimes like to crawl up pipes).

I hope that you enjoyed this introduction to greywater. Greywater systems are not for everyone, but I hope that in the future, new homes will default to having separate collection plumbing so that more people can at least have the option of saving water.

In this post and throughout the rest of this series, I use Art Ludwig’s The New Create an Oasis with Greywater as my primary source; it’s considered one of the best resources on residential greywater for the lay reader. Other bits and pieces are mostly pulled from my memory of other books and websites I’ve read. Any mistakes are, of course, my own.

Greywater practicalities: Distribution

Once greywater is collected, it needs to be moved into the landscape. At its simplest, the distribution system could be a bucket that you manually lug to the relevant part of the landscape. However, such a distribution system is hard to use and has health concerns.

Given concerns about ease of use, ease of maintenance, health, and efficiency, the distribution system is probably the most technically challenging aspect of a greywater design system. As such, I'll just cover the bare bone basics.

Most greywater distribution systems involve a series of pipes. The simplest systems take advantage of gravity to help water flow from the collection point to the receivers. These systems require the pipes to slope. The exact configuration can be finicky. If the slope is too shallow, the water will not flow. If it is too steep, the water will run ahead of the solids (lint, hair, food particles) leading to an eventual clog.

More complicated systems can be pressurized, although some pressurized systems require filtering to get rid of any solids in the greywater. Pressurized systems can move water uphill or along areas with too shallow a slope at the cost of energy and complexity. Some pressurized systems can safely water lawns by providing water underground. However, pressurized systems tend to break more easily and are significantly more expensive.

Whether pressurized or gravity driven, the distribution system should be designed with maintenance in mind. There are lots of good tips for maintainable distribution, but there are a couple key points. First, make sure you know where your pipes are (they’ll be hard to find after they’re buried). Second, make sure that you have access points for inspections, clog removal, and other maintenance tasks. Depending on how you’re using the greywater, it may also be worth designing the system to be reconfigurable in full or in part.

In this post and throughout the rest of this series, I use Art Ludwig’s The New Create an Oasis with Greywater as my primary source; it’s considered one of the best resources on residential greywater for the lay reader. Other bits and pieces are mostly pulled from my memory of other books and websites I’ve read. Any mistakes are, of course, my own.

Greywater practicalities: Collection

The last three posts in this series are going to get a little technical (but still not very). If you only care to know the general gist of greywater, you can stop here. If you want to know a bit more about how a greywater distribution system works, read on!

A greywater system has three subsystems: collection, distribution, and receiving. Each subsystem impacts the others, but for the sake of simplicity, I'll consider each separately.

Collection is the process of gathering the greywater. Greywater plumbing should follow all of the relevant plumbing codes, but instead of mixing greywater and blackwater shortly after they are produced, a greywater collection system keeps the two separate. Like any major plumbing change, collection plumbing is easier to add at construction time or when you already have the walls open to modify plumbing. As such, it's worth doing during construction even if the water initially is all sent to the sewer.

The most important factor to consider for collection plumbing is conserving fall. Fall is the vertical distance your pipe travels. Since greywater systems generally rely on gravity to move water, you want the points where your collection plumbing exits the house to be higher than for the sewer system (which generally exit under ground). Make sure your plumber conserves fall much more aggressively than they normally would.

Collection plumbing needs to have overflow into the sewer system. In addition to the overflow, it's generally a good idea to add a manual diverter near the point where the collection pipes exit the house. This allows all greywater to be sent to the sewer if needed (e.g., if you only need the greywater seasonally). If you are designing a system that will also handle dark grey water from the kitchen sink or a diaper-washing-clothes-washer you can add additional diverters to allow selective water diversion. All diverters should be easily accessible or they'll never be used.

In the simplest systems, water flows directly from the collection pipes to the distribution system. But not all distribution systems are equipped to handle a large surge of water (e.g., from draining a bathtub and clothes washer at the same time). A surge tank slows the rate at which water enters the distribution system.

The opposite problem can also occur: the amount of water at a particular time is not enough to effectively flow through the distribution system. In this case, a tank can collect water and then dose the distribution system with a single large flow when enough has built up. Both surge protection and dosing require care to ensure that the water does not sit too long — think a maximum of hours, not days.

Tomorrow we'll explore greywater distribution.

In this post and throughout the rest of this series, I use Art Ludwig’s The New Create an Oasis with Greywater as my primary source; it’s considered one of the best resources on residential greywater for the lay reader. Other bits and pieces are mostly pulled from my memory of other books and websites I’ve read. Any mistakes are, of course, my own.

Greywater goals

There are lots of reasons to use greywater^[1], and every greywater system will have a different combination of motivations, goals, and constraints. Greywater systems are not one-size-fits-all so it’s important to understand what you want before you choose a particular system.

Our primary goal is to reduce the amount of water we use in maintaining the fairly extensive gardens we hope to have. Our secondary goal is to reduce the amount of waste water we send to the sewers. Our primary motivation is practical — I hate wasting water that can be put to perfectly good use. Secondary motivations are environmental (reducing water use and sewage treatment volumes) and financial (saving on summer watering).

Because practicality is my primary motivation, we want a system that is fairly easy to maintain and fairly inexpensive to install and maintain. This means that we plan to limit myself to quantities and qualities of greywater that can effectively be processed by a garden. Since storage requires delicate and expensive filtration and purification systems, we’ll focus on a system that allows us to divert water directly to the garden when needed and to the sewer when it is not needed.

As we’ll see in the next post, these motivations, goals, and constraints make it a lot easier to decide what type of greywater system is right for us.

^[1]The legality of these uses varies by jurisdiction. In general, regions in the US that do have real water problems seem to have more flexible and realistic regulations than places that don’t. Be sure to check with local regulations before building a greywater system.

In this post and throughout the rest of this series, I use Art Ludwig’s The New Create an Oasis with Greywater as my primary source; it’s considered one of the best resources on residential greywater for the lay reader. Other bits and pieces are mostly pulled from my memory of other books and websites I’ve read. Any mistakes are, of course, my own.

Shades of grey: Greywater health and safety

Conversations about greywater often start with questions: Is it safe? What about disease? Greywater is safe, but we do need to take precautions.

First, let’s talk a bit more about greywater and blackwater:

• Greywater: Waste water with a low level of solids and a very low level of pathogens or toxic chemicals. Sources: washing machines, showers, tubs, bathroom sinks.
• Dark greywater: Water with a moderate level of solids or a low level of pathogens or toxic chemicals. Greywater turns into dark greywater if it sits for prolonged periods. Sources: Washing machine water used for diapers, kitchen sink water with small amounts of garbage disposal use, greywater stored too long in a tank.
• Blackwater: Water with a high level of solids, pathogens, or toxic chemicals. Sources: Toilet water or water from a sink that has cleaning chemicals poured into it.

Blackwater and dark greywater both can, under certain circumstances, be handled at home, but it requires lots of caution and more complex systems. I plan to ignore both for the rest of this series.

That leaves us with greywater. Greywater is not very contaminated. One statistic I saw claimed that residential greywater in the US has about the same level of pathogens as drinking water in some drought ravaged third world nations. That’s not a good thing — there are very good reasons that improving access to clean water is an important philanthropic goal — but it does illustrate that the contamination in greywater is something to be managed, not feared.

The low level of contamination in residential greywater in the US can be processed by the microorganisms in the soil, but every greywater system should follow basic guidelines to ensure healthy treatment. Ludwig’s book presents two fundamental guidelines for safety:

1. Greywater must pass slowly through healthy topsoil for natural purification to occur.
2. Design your greywater system so no greywater-to-human contact occurs before purification.

From these general principles, many specific principles can be derived: don’t add non-biodegradable chemicals to your greywater, get it quickly into the soil, don’t use it to water food plants, don’t spray it directly on plants such as grass, etc.

But the bigger point is that when it comes to greywater, both disregard for health concerns and excess obsession with health concerns should be considered errors. Education combined with careful design and management can produce a safe home greywater system.

In this post and throughout the rest of this series, I use Art Ludwig’s The New Create an Oasis with Greywater as my primary source; it’s considered one of the best resources on residential greywater for the lay reader. Other bits and pieces are mostly pulled from my memory of other books and websites I’ve read. Any mistakes are, of course, my own.

Why greywater?

We live in the Pacific Northwest where we have the good fortune of an abundance — some might say overabundance — of rain. But not all climates are so fortunate. Some parts of the world have almost constant water shortages due to degradation of the local water supply or a population which exceeds the water capacity of the region. Even in the northwest, we have to occasionally worry about drought, and no one likes high summer water bills.

On the other side of the coin, most homes in the US dump hundred of gallons of water into the sewer system every week. Some of this water is blackwater, which is any water that contains high levels of pathogens, e.g., toilet water. But the vast majority is greywater, which is water that has only a small amount of contamination, such as laundry or hand-washing waste water. Since black and greywater are mixed in most sewage systems, municipalities have to invest in expensive treatment plants which treat the whole slurry as if it were blackwater.

So here we have two problems: water shortages and sewer system load.

As is often the case, this problem can be mitigated by turning waste into a resource:

By separating out greywater from blackwater, we can reduce our residential water usage and reduce the load on our sewer systems. It’s a win-win!

In the next posts, I’ll give a high level overview of some of the concerns around greywater reuse and some practical tips about greywater systems.

In this post and throughout the rest of this series, I use Art Ludwig’s The New Create an Oasis with Greywater as my primary source; it’s considered one of the best resources on residential greywater for the lay reader. Other bits and pieces are mostly pulled from my memory of other books and websites I’ve read. Any mistakes are, of course, my own.