Off-grid living can be challenging ... but wait, what grid are we talking about here? Even rural homes are connected to a number of utility and communication systems without which, well, ... we would feel uncomfortable to say the least.
There are electricity, gas, telephone and cable TV connections. But the absence of potable water and a sewage system to contain infectious agents would threaten us more personally than the absence of any other connection.
It has been pointed out on this site that water systems are dangerously dependent upon energy and negatively impacted by climate change. This is true. The Pacific Institute estimated that each cubic meter of water (280 gallons) requires 1.06 kWh in the Northern California water system. The equivalent for Southern California is 3.35 kWh. Water related applications use 19% of the total electricity, 32% of natural gas and 88 million gallons of diesel in the State of California alone. Imagine what would happen should that energy no longer be available...
But how viable is it to be 'off-grid’ with water? There are low-tech solutions which are a throwback to the way many of our great-grandparents must have lived: a well, a hand pump, water pails and outhouses. I volunteer that 99% of the population would rather take their chances with the water grid than revert back to that standard of living.
Instead, consider Singapore for a moment. A highly developed city state with 6,489 inhabitants per km2, the second highest density in the world, it is chronically short of water. However, Singapore is notable for having some of the highest quality tap water in Asia. Singapore has implemented a “Four Taps” water strategy to decrease its reliance on water imports from Malaysia.
Four Taps Strategy:
Tap 1: Local rainwater catchment
Tap 2: Desalinated water
Tap 3: NEWater
Tap 4: Imported water
Now let us transfer Singapore’s strategy to a suburban home in Germany. In this temperate country, the average family of five uses 228 m3 per year:
Tap 1: Collect rainwater runoff from a standard-sized roof in an underground cistern. When calculating the expected runoff using local climate models, I arrive at 67 m3 per year; enough to cover 29% of the family’s needs. In order to use this water in the kitchen or bath, one would have to install a membrane based water filter.
Tap 2: The desalination ‘tap’ is not available
Tap 3: Singapore produces potable water (NEWater) from sewage ( ... there I said it). The water is filtered in traditional sewage plants, subjected to membrane-based microfiltration, filtered with reverse osmosis membranes and treated with ultraviolet light. NEWater is so pure that electronics manufacturers use it in wafer production processes and it is bottled.
In my imagined system, the home would use less technology to achieve a similar effect. A small Membrane Bioreactor (MBR) system could filter the sewage on the property so that effluent can be used for clothes washing, irrigation, swimming pools and toilet flushing. I assume that this system will achieve a rainwater reuse rate of 2x, stretching available rainwater to 58% of expected use, or 134 m3.
Tap 4: This is the ‘plug’ in my system, the five inhabitants are still short 94m3. Subject to a reuse rate of 2x, the home needs only 47 m3 (21% of total use) from the local utility.
According to the USGS, a five person household in the US would use around 551 m3 per year. Applying the same system, the US home would require 209 m3 from the water grid, or 38% of total use.
Notice that the system has not saved any water by installing low flow toilets, water saving shower heads or drip irrigation etc. These relatively cheap water saving devices will allow further reductions in water use. Increasing these savings or the reuse rate will allow moving the German home off the water grid entirely without excessive effort. The US home will require larger savings, higher reuse rates, more rain (or a larger roof) to move off the grid.
The primary criticisms of this system are the following:
The primary advantages are the following:
As Linda Richman (aka Mike Myers) of Saturday Night Live might have said: “While water is essential, the water grid is not. Discuss!”