Reduction of Water Used in Sewage Systems in Permaculture

Permaculture Designers Manual



Section 7.4 –

Reduction of Water Used in Sewage Systems in Permaculture

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In cities, water is chlorinated and fed back into the system, sometimes mixed with seawater or “treated” waste water to give it that city taste so typical of, e.g. Las Palmas in the Canary Islands.

Surplus sewage, untreated, is often passed to sea, with bacteria and parasites intact for bathers to wallow in.

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All of this arises from the frequent, wasteful and unnecessary flushing of toilets by those of us living in the effluent society.

In Sweden, it is compulsory to use dry toilets in remote, un-sewered or unsuitable areas.

In the USA, UK and Australia, one has to fight hard to get permission to use these, as it is the vested interest of industry and town clerks to supply and charge for sewerage systems.

However, no clean water need be used to flush toilets if there is a diversion from a hand-basin to the toilet tank.

In Australia at least, hand-basins molded in to toilet flush tanks are available (Figure 7.31).

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It is essential to use low-flush toilet bowls with such systems, as they otherwise flush incompletely and build up heavy pathogenic bacteria populations.

This is a simple solution to 40% of domestic water misuse and encourages hand cleanliness rather than the false cleanliness / tidiness of toilet flushing for its own sake.

Dry toilets are not always appropriate, except in cities and other water-critical areas.

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They are unnecessary on farms or in well drained soils or wherever sewage is used to produce methane by anaerobic digestion in tanks.

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In fact, dry toilets reduce the potential uses of sewage, just as compost is a reduction in the potential use of mulch.”

Dry toilets are quite specifically useful where:

No methane system is used;

Sewage is not used in the production of plants;

Soils do not suit septic tanks;

Cities have critical water supply problems.


In using wastewater from kitchen, bathroom and laundry, it is wise to establish just what chemicals, and at what concentration, is being released to gardens and soils (or waterways).

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A typical analysis of a powdered detergent or a soap could include: sodium or potassium salts or poly-sulfates, silicates, sulfates or bicarbonates, borates, residual biocides (concentrated in animal fats) e.g. DDT, Dieldren, Hexachlor from dairy cattle, additives such as resins (hardeners), scents, dyes and brighteners, fecal bacteria and viral or worm pathogens from washing (in showers or via clothes). This data is from Kevin Handreck, CSIRO Division of soils. (pers. comm. 1979)

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Of these, most can be dealt with by soil organisms, but if the basic water supply is already saline, sodium and potassium salts can add to this and de-flocculate soil clays or damage leaves (at >1,000ppm), while borates at >0.5ppm can create excessive boron concentration in soils and above 1.0ppm is harmful to soil life and plants.

Thus, we need to use plain soaps on crop if possible and route more complex pollutants to tree systems (well-monitored), as woody perennials can cope better than garden vegetables and allow more time for decomposition of long-term pollutants.

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In critical areas, and especially in arid or delicate environments, we may need to create both special soaps (unpolluted oils, potash or sodium) and plant special crops which remove excesses (many water plants) before passing on grey water to the soils and streams.

There is no blanket policy, only specific cases where we can expect to gain yield and also clean up water if we know the composition of soils and soaps.

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