What is Greywater?

Greywater is simply used wash water from the bath, shower, sink or even rooftop rainwater harvesting; this is slightly polluted, very different from either potable (freshwater) or non-useable sewage water (blackwater).

Clean water is water with nothing but H2O, greywater has been used once for non-toxic cleansing, but blackwater carries pathogens that are too strong and unsafe for either animal or plant consumption.

But why is greywater important to us? The main reason is sustainability. The closer and closer our nation comes to becoming self-reliant and independent of foreign oil, the closer we come to understanding what energy efficiency is all about.

Making use of our nation’s abundant greywater production could potentially solve our water conservation issues, and bring us just that much closer to self-reliance and a more sustainable and healthier future for the children of our children.

What determines the main differences between blackwater and greywater are nitrogen and pathogen content as well as decomposition time.

Basically, once polluted with human fecal material the pathogens find a place to thrive and reproduce in any body of water, therefore, the best solution is simply NOT throw human fecal material in water in the first place, but our society is essentially Roman, with Roman practices.

Plumbing or “lead working” is part of ancient megalithic architecture and the word itself is of Latin origin, coming from plumbum related to the Greek “molybdos” (probably of an extinct Mediterranean language such as Iberian perhaps).

However wonderfully advanced they were to have invented such uses for “lead” as piping freshwater from the mountains into public bath houses and developing the very first spas on earth; such wonders have a price on ecology…

A price that haunts us even now…

In most bathhouses of those times; private “water closets” were also readily available for those bathing, but where did the water go from the water closet? Was the destination the same as the bath water?

The Romans and eventually the English would readily sacrifice a nearby river for ALL the wastewater used in the bathhouses (including that from the water closets).

An ecologically unsound and unsustainable practice that we still have to this very day

With modern methods of plumbing, this is no longer necessary, but our society continues to throw such radically different substances into the same shaft; polluting greywater, both due to force of habit as well as lack of knowledge

But that needs to change, and the solution is separating our greywater from our blackwater, NOW, not tomorrow when it’s too late.

The amount of nitrogen and human fecal materials found in blackwater is absurdly difficult to remove sustainably if not incredibly impossible at the moment.

Nine tenths of the nitrogen found in our nations combined wastewater is contaminated by blackwater, and most of that water was originally greywater before entering the city’s sewer system.

Engineers argue in most scenarios that wastewater, including greywater, if left untreated, will soon become anaerobic and foul, taking on the same characteristics as blackwater, which is why greywater must be treated quickly and in-house if not possible in-community.

The secret to really defeating the pollutants in greywater are oxygen breathing organisms like algae that thrive off of nitrogen and carbon. Problems occur however when the greywater is left to become anaerobic, then, yes, it is as unsafe as blackwater.

An excellent study done in Stockholm with a separated greywater/blackwater plumbing system in a multi-apartment complex (made by Lars Karlgren, Victor Tullander, Torsten Ahl and Eskil Olson) collected data for 12 weeks and discovered the following results.

Their article entitled “Residential Waste Water” reported that this small community could divide its greywater production into 30 gallons a day laundry wastewater, 20 gallons a day kitchen wastewater, 60 gallons a day bath wastewater and 10 gallons per day miscellaneous wastewater, coming to something like 56% of the total combined wastewater consumption of any given household per day.

The other 44% or so of wastewater was all blackwater from either the garbage disposal unit or simple toilet flushing; coming to a grand total of 80 gallons per day of blackwater!

Statistically that means that only 44% of the water being treated at the sewage facility was originally blackwater, the majority then was originally greywater? Why pollute that much greywater? Because our traditional combined wastewater system is too old, too Roman.

According to this study, on the average, if separated we would find that 56% of all our world’s sewage water is originally greywater and greywater uses far less energy to be properly treated than blackwater, meaning we are spending at least 56% more energy to treat our combined sewage than necessary with today’s modern technology!!

So, how can greywater be properly treated at home and harvested for reuse, irrigation or the safe replenishing of the aquifer?

A simple method for greywater harvesting is simple pre-treatment that dumps directly into a soil-box planter, which then produces useful irrigation water.

A more advanced greywater treatment system on the other hand, for those with more space could contain a septic tank, a sand filter, a pump and of course a planter bed, to then revert the treated water into field irrigation or even reused in the house as desired.

Depending on how much mechanical and biological filtration is done will depend on how potable greywater can be in final stages.

Chemical cleansing of greywater is at the very least undesirable, as greywater in most cases is already very close to drinkable before any filtration, but chemical filtration if done would be the final stage, usually in the form of chlorine treatment (not a completely sustainable alternative due to the chemical manufacturing process).

Aside from irrigation, and returning filtered greywater back to the ground reservoir cashes, a more immediate and sustainable use for already filtered greywater is returning it to the household tap from whence it first originated.

In this manner, while some greywater can’t be recovered, an average of 56% of the total household use is saved daily. Just imagine, 56% water savings per day, on laundry, bath and the kitchen sink alone!

Investing in a greywater harvesting system means a little remodeling, extra plumbing and finding garden space enough for the mechanical and biological filters, but once properly treated, greywater can be harvested by refueling one or two water boxes used only for the greywater system; preferably the bathrooms (even the toilets) and laundry room.

Unless you can be sure that the water is drinkable, the kitchen is not recommended as a redirect tap, but the bathroom toilet, bath and sink are all recommended, as well as the laundry room, as even the simplest methods of filtration should be enough for these uses in most households.

As with any controlled system of waste separation, each thing has its place, so if a system such as the above is of particular interest to you, don’t do anything like drink from the bathroom sink (as the water is still recycled greywater) or pour spoiled vegetable soup down the kitchen sink drain unless its in the garbage disposal organic matter mixed with water becomes blackwater immediately.

All in all, greywater harvesting is definitely a suggestion for a more sustainable tomorrow, as the water is treatable at home, and need not be combined with blackwater.

Greywater is reusable and one more of our earth’s precious resources, to be used wisely with economy and ingenuity for the needs of the now, predicting the needs of the future in one single detail, sustainability.


Posted in Methods by Administrator on January 5, 2007.

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