As water filters through the biological surface layer of soil, it is purified by microorganisms and plant roots.
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Greywater Recycling Basics
What Is Greywater?
Greywater is any
household wastewater with the exception of wastewater from toilets, which is known as blackwater. Typically, 50-80%
of household wastewater is greywater from kitchen sinks, dishwashers, bathroom sinks, tubs and showers. Of course,
if you use a composting toilet, 100% of your household wastewater is greywater.
Freshly generated greywater is not as nasty as blackwater, but if it's not handled properly it can soon
become so. Greywater decomposes at a much faster rate than blackwater and if stored for as little as 24 hours, the
bacteria in it use up all the oxygen and the greywater becomes anaerobic and turns septic. After this point it is
more like blackwater - stinky and a health hazard. In fact, many jurisdictions have strict regulations about disposal
of greywater, some even require it to be treated as blackwater.
Not all greywater is equally "grey". Kitchen sink water laden with food solids and laundry water that has
been used to wash diapers are more heavily contaminated than greywater from showers and bathroom sinks. Although greywater
from these sources contains less pathogens than blackwater, many regulatory bodies consider it as blackwater.
The safest way to handle greywater is to introduce it directly to the biologically active topsoil layer, where
soil bacteria can quickly break it down, rendering the nutrients available to plants. This biological water purification
is much more effective than any engineered treatment, thus protecting the quality of groundwater and surface waters.
Benefits of Greywater Recycling For Irrigation
- Reduce fresh water use - When the weather is warm, about half of the water consumed by the average household in North America is for outdoor
use. Capturing the indoor greywater for use outdoors can cut water usage in half.
- Reduce strain on septic system or treatment plant - Greywater makes up the majority of the household wastewater stream, so diverting it from the septic system
extends the life and capacity of the system. For municipal systems, decreased input means more effective treatment
coupled with cost savings.
- Develop otherwise unsuitable real estate - A greywater recycling system, along with the use of
composting toilets, can enable the development of property that is unsuitable for a septic system.
- Groundwater Recharge - Greywater recycling for irrigation replenishes groundwater, helping the natural hydrologic
cycle to keep functioning.
- Plant growth - Greywater can support plant growth in areas that might otherwise not have enough
- Maintain soil fertility - The nutrients in the greywater are broken down by bacteria in the soil
and made available to plants. This helps to maintain soil fertility.
- Enhance water quality - The quality of groundwater and surface waters are much better preserved by
the natural purification processes the greywater undergoes in the top layers of the soil than by any engineered water
- Satisfaction - The greywater user gets the satisfaction of direct participation in the responsible
management of global nutrient and water cycles.
Greywater Irrigation May Not Be A Good Choice If:
- Soil is not suitable - If your soil is either too permeable or not permeable enough, you may not be able to
recycle your greywater, or you may need a system with some modifications.
- Area too small - You need enough soil to process the greywater and enough plants to use it.
- Climate unsuitable - If it's too wet to benefit from irrigating with greywater, there may be a better way to
dispose of it. If it's too cold, you will only be able to recycle in the warmer months. In cold climates, the heat in greywater
may be more valuable than the water itself. See Drain-water Heat Recovery.
- Permit hassles - Many jurisdictions in North America have no clear guidelines regarding greywater
processing. With water shortages looming in the near future for many regions, this may change sooner than later.
Health concerns are often cited as the reason for not allowing greywater recycling, although there has never been a
documented case of somebody becoming sick as a result of exposure to greywater.
- Low cost/benefit ratio - Where legal requirements dictate a complex system and there is only a
small flow of water, greywater recycling is not economically feasible.
- Inconvenience - If the greywater system you are considering is more expensive and requires more
maintenance than a properly functioning septic or sewer system.
To recycle greywater safely, users must understand the nature of the grey water
itself as well as the natural cycles and processes involved in the purification of it. Each set of circumstances
requires its own unique recycling system for optimum results.
For most residential purposes, low-tech, home made grey water systems
tend to outperform and outlast expensive pre-made systems.
Greywater Recycling Health Concerns
Health risks are often cited by regulators as reasons for requiring high-tech
expensive systems although there are no recorded instances of greywater–transmitted illness in the US. However,
greywater may contain infectious organisms. Bear this in mind when designing and using a system. A poorly designed
system could become a pathway for infecting people.
Two main principles for safety:
- Greywater must pass slowly through healthy topsoil for natural purification to occur
- Design your greywater system so no greywater-to-human contact occurs before purification
(ie: passing through the soil or mulch basin)
- Prevent contact or consumption - Avoid accidental connections between freshwater and greywater plumbing
- - Label greywater plumbing, including garden hoses
- - Use gloves when cleaning greywater filters
- - Wash your hands after contact with greywater
- Microorganisms on plants - Don’t apply untreated greywater onto lawns, or fruits and vegetables that
are eaten raw (eg. strawberries, lettuce, carrots)
- Breathing of microorganisms - Don’t recycle untreated greywater with sprinklers. Droplets can evaporate
leaving harmful microorganisms in the air where they can be breathed in
- Use only greywater that is fairly clean to start with - Greywater containing water used to launder
diapers or generated by anyone with an infectious disease should be diverted to a sewer or septic system
- Don’t store greywater - Use it within 24 hours before bacteria multiply. After 24 hours it is well on its
way to becoming blackwater
- Don’t overload your system - If you’re having company and your system is designed for 2 people, divert
the greywater to the sewer or septic system for the evening
- Chemical contamination - Don’t buy household cleaning products you wouldn’t want in your greywater system.
Divert greywater containing harmful chemicals to the sewer or septic system
- Prevent contamination of surface water - Discharge greywater underground or into a mulch filled basin
- - Don’t apply greywater to saturated soils
- - Apply greywater intermittently so it has a chance to soak in and the soil can aerate between waterings
- - Confine greywater to subsurface or mulch basins at least 15m from a surface waterway
Elements Of A Greywater Irrigation System
- Greywater source(s) - Washing machine, shower, bathtub and/or sinks
- Collection plumbing - Pipes that transport greywater from inside the house to just outside the house
- Surge Tank, filter and pump - Optional elements that add complexity and cost but make the distribution plumbing's job easier
- Distribution plumbing - Pipes that transport greywater from just outside the house to locations throughout the receiving landscape
- Receiving landscape - Soil, roots, plants, and mulch basins that contain, cover, purify, and use the greywater
- People - Those who design, make and maintain the system, generate the greywater, tend the garden and eat the food it produces. People
are a critical but often overlooked component of the system
Types of Greywater Irrigation Systems
Drain To Mulch Basin
- no filter
- no pump
- no surge tank
- uses very little pipe
- little or no maintenance
- low economic cost
- low ecological cost
- anyone can build it
- failure rate is low
- lasts forever
- same as drain to mulch basin
- higher economic & ecological costs are offset by capacity to handle higher volumes of greywater
- uses multiple mulch basins
- contains & covers greywater in the landscape
- automatically disperses greywater to several locations
- ideal for wet climates
- good where soil perk is low and space is restricted
- good for treating larger volumes before reuse
- poor choice in dry climates
- reduced reuse efficiency due to uptake by wetland plants
- efficiently treats blackwater as well as greywater
Solar Greywater Greenhouse
- highest ecological net gain for cold climates
- allows year-round treatment of greywater
- solar greenhouse helps heat the house
- food production
- conserves the heat in the greywater
Other Suggestions For Cold Climate Greywater Irrigation
- continuous downhill slope in all plumbing
- no standing water so there's nothing to freeze
- heat in the greywater may keep pipes in the distribution plumbing clear into the frost season if there is sufficient insulation (mulch, leaves etc.)
- minimum 6 inches fall at discharge outlets to prevent ice buildup clogging outlet
- ground should slope sharply away from the outlet at first, then may gradually flatten
- apply the greywater in a warmer microclimate, eg. the south and west side of a house with a windbreak to the north will be significantly less frosty and may extend your irrigation season
Greywater As A Heat Source
- in cold climates, the heat in the greywater may be its most valuable aspect
- Drain-water heat recovery extracts heat from shower drain water and use it to preheat water entering the hot water heater. Click here for more information on drain-water heat recovery.
Choose The Right System For You
Greywater systems are very context-dependent. There is no universally ideal system. Choose your system based on:
- greywater sources
- irrigation needs
- soil percolation rate
- water availability
Before You Start: Get Clear On Your Goals
- What is your overall environment? Upscale neighbourhood or a country cabin?
- What other lifestyle changes are you willing to make regarding water conservation?
- What is your standard of perfection?
- Are you trying to use or dispose of your greywater?
- How important is it to increase reuse efficiency?
- Expected economic payback time
- Landscape goals
- Other goals
Common Greywater Errors
- Assuming it's simple - Failure to realize that a greywater irrigation system that achieves your goals
is a site-specific and user-specific design issue almost any other green home technology
- Out of context design - Constructed wetland in the desert or irrigation of a swamp
- Overly complex, delicate, or expensive system - A typical residential greywater system saves
$5 to $20 worth of freshwater per month. If the system costs more than a few $1,000 the owner and the earth
are probably better off wasting the water than the pumps, valves, fittings, piping, filters, and electricity
- - During drought, or where water is otherwise unavailable
- - Where there are acute water disposal problems
- - Where a high volume of greywater co-exists with a high need for
- Mansion with a greywater system - The value of the greywater is negligible compared to the other waste.
Trying to capture the greywater just adds more waste in the form of hundreds of feet of extra plumbing
- Pump zeal - Pumps won't work without filtration and filters clog quickly due to the high solids content in
greywater. Pumps shorten the life of your system, and you may be substituting electricity waste for water waste
- Storage of greywater - Bacteria multiply to blackwater levels very quickly
Conserve Water First - Before implementing any greywater system, be sure you have taken all possible measures to conserve water, for example:
Follow Ecological Design Principals - The greatest efficiency (and quality) is achieved when the power of the tool is well matched to the task at
hand. Choose the simplest design that meets your needs and build it as well as you can. Consider the ecological cost of the system components.
- low flow shower heads
- low flush/composting toilets and "If it's yellow let it mellow" policy
- aerators on faucets
- efficient front loading washing machine
- natural landscaping
- rainwater harvesting
The information on this page is used with the kind permission of Art Ludwig.
Art is an ecological systems designer who has done extensive work with greywater systems. For more information,
please visit his website www.oasisdesign.net
where you'll find more than 300 pages of information about greywater as well as the leading books on