http://www.greeneducationfoundation.org/green-building-program-sub/learn-about-green-building/1230-greywater-systems.html

My concern would be over what goes into the grey water to make it grey. I think sustainable grey water systems should operate against a backdrop of environmental regulations on the types of detergents and other contaminants that are permitted. It's not clear to me that septic-tank sand-filtering systems will prevent certain contaminants from getting into the ground water and maybe the most worrisome contaminants can be more efficiently dealt with on the industrial scale of centralized sewage treatment plants.

Dr. Karl Pfeifer septic tank water may not be reused as grey water.it may be pumped to the treatment plants to be used in power plant generation.

Oh. Aren't there septic systems that deal with grey water and toilet water separately? Anyway, your diagram shows the grey water ending up as ground water under the planter bed and that was my worry -- what remains after treatment and goes into the ground water?

By "reuse as grey water" do you mean diverting the water before it enters the septic tank? Again, that would worry me if it's used for irrigation since contaminants in the grey water would get into food and into the water table. Better to irrigate with collected rainwater instead of grey water. However, if the grey water were used for flushing toilets into the septic tank, that would (possibly) be okay if the water were pumped into a sewage system that leads to large scale treatment plants.

Where I used to live, water came from the river running through the city and was treated to make it drinkable. Grey water and toilet water went into the sewer system, where it was treated and pumped back into the river and ultimately became part of the watersupply of other communities downstream. I guess I have more faith in industrial scale treatment than in very localized treatment such as households, farms, or apartment blocks.

The farmsteads of my youth mostly had septic systems with a "septic field" for filtration. The septic tanks were pumped out with a tanker truck every so often, which then emptied their load into a field or bushland without concern for contaminants ending up in the soil and groundwater. Since the households also all used well water, no doubt a lot of contaminants ended up in what people ate and drank and likely caused some of the cancers in people I grew up with.

http://www.greeneducationfoundation.org/green-building-program-sub/learn-about-green-building/1230-greywater-systems.html

" What Can Greywater Be Used For?

With proper treatment greywater can be put to good use. These uses include water for laundry and toilet flushing, and also irrigation of plants. Treated greywater can be used to irrigate both food and non food producing plants. The nutrients in the greywater (such as phosphorus and nitrogen) provide an excellent food source for these plants.

What Are The Benefits of Greywater Re-use?

Re-using water does not diminish our quality of life, however it can provide benefits on many levels.

Two major benefits of greywater use are:

• Reducing the need for fresh water. Saving on fresh water use can significantly reduce household water bills, but also has a broader community benefit in reducing demands on public water supply.
• Reducing the amount of wastewater entering sewers or on-site treatment systems. Again, this can benefit the individual household, but also the broader community"(https://www.sustainable.com.au/greywater-treatment)

Following answers

" What is green building?

A ‘green’ building is a building that, in its design, construction or operation, reduces or eliminates negative impacts, and can create positive impacts, on our climate and natural environment. Green buildings preserve precious natural resources and improve our quality of life.

There are a number of features which can make a building ‘green’. These include: 

• Efficient use of energy, water and other resources
• Use of renewable energy, such as solar energy
• Pollution and waste reduction measures, and the enabling of re-use and recycling
• Good indoor environmental air quality
• Use of materials that are non-toxic, ethical and sustainable
• Consideration of the environment in design, construction and operation
• Consideration of the quality of life of occupants in design, construction and operation
• A design that enables adaptation to a changing environment"(https://www.worldgbc.org/what-green-building)

Many good answers here.  The whole conversation depends on the availability of clean water - Ottawa, Canada, for example, has a reasonably clean river flowing past it at a minimum flow rate of 500 cms (and upstream reservoirs that can provide that flow for more than a year).  The City takes 5 cms - it will never have a problem providing domestic water. 

I would add that a 4-water system may be useful to think about where ample clean water is not available.

• Black water - expected to be contaminated with biology, chemistry, and suspended solids.  Not suitable for reuse without biological treatment and physical filtering (eg, septic tank and tile field)
• Grey water - expected to be contaminated with chemistry and suspended solids.  Not suitable for reuse without fine filtering, but not considered potable without further treatment.  Can then be used for flushing toilets and watering plants.
• White water - not expected to be contaminated, and not treated further before non-potable uses:  Fire fighting, maybe domestic hot water (if kept above 55C to eliminate pathogens)
• Blue water - clean water, treated to eliminate pathogens and/or toxic chemistry.  Reverse Osmosis, ozonation, chloramine, etc.

Rain water would be considered grey water, but would be really simple to clean to white water.  White water could be treated at point-of-use to be blue water.

In an urban setting, there would then be 4 pipes coming from the street to service the home.  White and Blue in, Black and Grey out.  Grey gets treated locally and stored locally as White water, and provides fire protection.  Stormwater ponds would be used to supplement grey water.  Etc.

Wonderful and useful discussion ,Douglas Nuttall,please send me more on my e-mail [email protected]

Thank you very much Dr. Mehdi for sharing opinion