Most local authorities will define the household’s size by either number of bedrooms or the number of permanent inhabitants. Whatever stipulates the law, it all comes down to the daily volume of generated wastewater (sewage) that must be stored, processed, and subsequently discharged over a leaching bed.
Typically, even municipal utility services do not measure volumes of generated wastewater by individual households. As the estimation, they use the available data for freshwater consumption per household (or per capita). While there is a good match for individual apartments, where freshwater is fully used for indoor consumption (what comes from faucets, showers, and flushing toilets must go down the drain), there will be a discrepancy for residential properties with gardens, swimming pools, outdoor spa, etc. Nevertheless – looking at statistical data, it is important to consider the following facts:
a. The average water consumption per household does not necessarily represent your case. Luxurious residential properties certainly use more water than typical ones (lavishness is wasteful and has its price…). Households in hot and humid climate zones will have higher indoor water consumption than those in moderate or colder climates (less frequent showers and laundry…).
b. Houses in rural locations without access to the Municipal Water System certainly use much less water than those in residential neighborhoods of big urban areas (note, that most Container-based Houses will be located in rural (if not remote) areas).
Many human habits are shaped by “because we can”. Each faucet fed by Municipal Water System and drain connected to Municipal Sewage System exactly represent such case – it is a limitless source of freshwater and limitless drain that will devour whatever we drop into it. And unless we live on a tight budget, not many will pay attention to how we use the water!
At “Off-grid locations” (here in a wider sense representing the lack of access to Electrical, Water, and Sewer municipal systems), suddenly we are facing the situation that all these resources are LIMITED, and we have to use them wisely! And such a situation (scarcity) quickly re-shapes our wasteful habits!
Indoor household water uses per capita by fixture (Source: “Residential end uses of Water”, Version 2 (slightly modified), April 2016, published by Water Research Foundation).
Quick math gives us some 58.6 gallons per capita. Fortunately, this number does not reflect the recent progress in the technology of domestic fixtures and appliances. Sensing the public sentiments (largely affected by rising prices of resources), manufacturers are introducing not only energy-efficient fixtures and appliances but also water-efficient ones. Modern toilets (by far the largest drains of water) come with dual- flush systems, washing machines with reduced water use, faucets with limited water flow, showers with cut-offs valves…. It’s important to notice, that all these measures do not affect our comfort of life, however, they significantly decrease the amount of consumed water and sewage as well as our bills. To put it in numbers, from 1999 to 2016 the average household water uses per capita decreased by about 15% (from 69.3 to 58.6 gallons per capita daily), but the potential for further improvement is still there. In fact, it is expected that the daily limit can be reduced to about 25 gallons per person.
You will find a relatively high level of leaks in the average American house. The good news is that leaks represent mostly old houses with equally old plumbing systems, so you can disregard them as a valid “contributor” to the amount of generated sewage. All in all, you can count on much lower water use in your new, off-grid container house. And what does not go down the drain, does not end up in the Septic System.
Note that we did not consider here water used for outdoor applications (landscape irrigation, washing cars, and pavements, outdoor spa, swimming pool, etc..). It must be taken into account in your budget of freshwater, but it does not go down the drain!
Classification of Wastewater
Traditionally, we assume that blackwater comes from toilets and greywater from everything else in the house.
Typical household’s sources of the black and greywater (note that here, the dishwasher is erroneously considered as a part of the greywater system). Source: “Sewage Treatment in Graywater Systems” by Sara Heger, (Onsite Installer magazine)
Well, it’s not exactly like that, because the classification of wastewater should be determined based on its content. From this point of view, household-generated wastewater includes:
Blackwater (flushing toilets and bidets).
It mainly contains human feces, urine, toilet paper, and cleaners (if used). The “black” represents a sort of “keep-away” message referring to highly odorous solids and potentially harmful microorganisms like microbes, pathogens, viruses, bacteria… It also contains traces of diluted chemical (cleaners) and pharmaceutical (drugs) compounds.
Raw blackwater cannot be released into nature. Given mostly organic nature of solids and contaminants, it can be treated in a natural (biological) decomposition process.
Greywater (shower, bathtub, bath sink, washing machine)
In general, it’s water mixed with disinfectants like soap, shampoo, conditioners, detergents, cleaners, personal care products (cosmetics, toothpaste, body lotions…), human sweat, solids (human hairs) … and the list can go on. These are mostly chemical products, some biodegradable. Usually, greywater is considered as a “low-risk” wastewater.
By “definition”, the raw greywater should not contain organic matter and microorganisms. It does not mean, however, that it can be released “as-it-is” into nature. Chemical compounds may be harmful to human health and when accumulated in larger concentrations – to the environment. Also, the bathwater, shower water, and water discharged by the washing machine (from soiled underwear) may have traces of human excrements and urine.
Fortunately, basic greywater treatment systems are much simpler than those for blackwater, and for typical end-user (flushing toilets and outdoor irrigation), relevant regulations are not too restrictive.
Dark Water (Kitchen sink and dishwasher)
Kitchen-originated wastewater contains organic matter (including fats and oils), as well as all sorts of detergents. The presence of bio-degradable organic matter and coming with it potentially harmful microorganisms does not allow us to classify it as greywater. The presence of chemicals, however, does not fit well into the otherwise organic nature of blackwater’s waste.
In many countries, kitchen-generated wastewater is considered as a “High-Risk Greywater” and it requires more complex treatment than greywater from bath and laundry. Typically, in split black-grey water systems, the dark water is collected by the sewer.
Individual sources of wastewater and their major contaminants. Source: “Domestic Greywater”, Lanfax Labs (Australia)
Typically, all household-generated wastewater goes down to common sewer pipe and then flows either to the Municipal Sewer System or an individual onsite Septic System. There are cases, however, when (despite the increased cost), it may make sense to not mix the two most dissimilar classes of wastewater – Black and Grey. And the reasons for that are:
Decreasing the demand for freshwater
Possibility to reuse greywater may be crucial for homes having limited access to freshwater (harvested rainwater as the only source),
Decreasing the volume of wastewater
It may be the only solution at locations where the size of the lot, its geological conditions, and the quality of soil have limited capability for the treatment of larger volumes of wastewater. Limiting the volume of wastewater, reduces the hydraulic load of the drain-field, its size, lifespan….
Growing “Eco-Consciousness” of our society!
This is probably the most important plan of action, that all of us should take seriously. The choice is simple – either we will leave the Blue-and-Green Planet to future generations, or rather the Scorched Land.
Eco-friendliness should become a permanent element of our lifestyles. Source: “The Complete Beginner’s Guide to Greywater Systems”, (Elemental Green)