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  • Posted April 29th, 2018

    Why flushing away ‘waste’ water is a bad idea, and what better options exist

    Why flushing away ‘waste’ water is a bad idea, and what better options exist

    Like many things in modern life, the vast majority of our current water and wastewater infrastructure is completely dependent upon fossil energy to keep the toilets flushed and the taps running. Even the word “wastewater” itself assumes that we have no better use for the water that we flush out of our homes or the nutrients and biomass it contains than to dump it. In a truly sustainable society, “sewage” would be a word of the past, and we would begin to hear terms not typically used in today’s media like “humanure” and “yellow water”. Humanure is fairly self evident, yellow water is the term used in Scandinavia for the nitrate and phosphate rich urine/flush-water mix from urine diversion toilets.

    Briefly, if the electricity supply in my home were to stop for a week, the first thing that would happen is that my children would enjoy candles and games for a day or two. We’d need to light the gas stove with matches instead of the electric sparker. I’d take a rest from desk work and move my attention to the garden. After a few days though the water supply would dry up, since the council pumps would no longer be able to replenish the reservoir. We have a rainharvesting system for the polytunnel, so we could boil that for drinking and cooking. Houses without rainwater collection would start to queue up to collect water centrally, as was the case in recent years when the mains froze in many parts of Ireland.

    Without mains, the toilet would run dry, which would be fine for anybody with a compost toilet, but not so comfortable for those without. After a while, if we were out walking by the river we might notice the lack of treatment as the council treatment works failed to treat the sewage which was being flushed towards it, washed along with a significant proportion of people’s hard hauled water. Countrywide this would contribute to significant sewage pollution of all of our rivers and estuaries and a large proportion of our streams.

    Septic tank and drainage field.
    Septic tank and drainage field.

    In terms of “water security”, we’re not really terribly well protected. In anything but the very short term, if there is a shortage of electricity, we’re in a fairly vulnerable position in Ireland, as are most affluent nations.

    However, there is another way that we can proceed from here to rebuild our water resilience. Rainharvesting can become relatively standard. It may well do so now that water charges loom large in people’s minds. A water butt or even large tank is not an expensive thing to install and provides water for garden use and a backup if needed for emergencies. The most beautiful water container I’ve seen is a house in Galway where the roof water is routed directly to a garden pond, which doubles as a reservoir for the household plumbing; pumped back in and filtered.

    I’ve often looked at sloping urban topography and itched to set up a gravity-fed water collection network where one house roof feeds to the header tank of the house below, via a sand filter. Even a more conventional rainharvesting scheme on a widespread basis would presumably have a lower environmental footprint than pumping Dublin’s water from the river Shannon.

    Compost toilet.
    Compost toilet.

    Sewage treatment can be completely zero energy if we use constructed wetlands and reed bed systems. Even septic tanks and percolation areas – well laid out in suitable soil conditions – are an effective and zero energy technology. Zero discharge willow facilities take a bit of pumping to get the septic tank effluent properly spread, but they can repay many times over in firewood value. With a properly laid out site, domestic sewage treatment needn’t need electricity at all. Where power is used to lift effluent to a higher level for disposal or treatment, then what I rather grandly term an “emergency response wetland” may be build down gradient of the main septic tank so that at least in power outs, any overflows are treated before reaching the groundwater or adjacent drains.

    As a municipal example of this, Mayo County Council have adopted such a system for Kiltimagh, where the town sewer discharges into a large municipal constructed wetland system for tertiary treatment. The main secondary treatment system (“secondary” meaning the oxygenation stage that follows “primary” settlement) is a standard mechanical, electrically powered system. However in the event of a storm surge (where excess rainfall diverts sewage around the secondary treatment system) the excess will be dumped in the constructed wetland for treatment there. The same would happen in the event of a power failure, but I’m not sure that was necessarily a design feature. All of the stormwater from the town also flows through the constructed wetland, so that the receiving river is much better protected than many others in the country.

    Something to consider with any discussion of sustainability and sewage is that once we mix resources, they become less useful. By composting faecal biomass and storing urine separately from flush water we can reuse these safely in agriculture. As a country, we have the potential to not only improve the quality of our water courses and groundwater resources, but to reduce our fertiliser import costs and associated ecological footprint as well. Many dry compost toilet designs are in use in Ireland and around the world already. For those who still want their resounding flush, the Swedish Aquatron and Dubbletten systems provide faecal separation and urine diversion for applications ranging from domestic to municipal level.

    Grey water is another consideration. Sewage is well known for it’s inherent toxicity, laden as it is with heavy metals and other contaminants which make sludge less than ideal for reusing in agriculture. From a sustainability perspective we may want to reuse such sludges in agriculture without causing problems, or we may want to reuse domestic grey water for irrigation on the garden; including on edibles. The only way to be sure of your food is to check the ingredients. If you keep harmful chemicals out of your sink then you can use the water on your fruit and vegetable beds. If you still want the latest cosmetics, cleaners and the chemicals that are in them; don’t reuse your grey water for anything other than fertilising your willow firewood crop.

    Newly-planted reed bed.
    Newly-planted reed bed.

    If we want sustainability as a country, then it would serve us well to check what products we welcome onto our supermarket shelves and perhaps tax those that have the biggest impacts. That way we both discourage the more harmful ingredients that end up in municipal sludges and raise the necessary capital to reinvest in more sustainable alternatives in the first place.

    Well what can we do, as individuals? In our own homes we can reduce our water needs; use a compost toilet or plumb up a water butt to our toilet cistern; reuse clean grey water in our polytunnel; or investigate the merits of a rainharvesting system, from both a cost and energy perspective.

    On a community scale we can explore our neighbourhood; check the possibility for using simple constructed wetlands to clean up obvious pollution sources; liaise with local community groups regarding our local water sources and examine how resilient they are. Nationally we can engage with the water issues that are ever-present in the media; we can lobby our locally and nationally elected representatives for sustainable water use and for effective, low or zero energy sewage treatment. Irish Water have already publicly expressed an interest in using reed beds and constructed wetlands[1].

    On a wider level we can consider our “water footprint”. It’s not something that many of us look at, but taking clothing as an example, hemp requires about 50% less water to grow than cotton, and only a quarter of the water needed for processing. Other similar comparisons are set out in the Water Footprint Network site http://www.waterfootprint.org. Fortunately, water is like many environmental choices we make, the more we buy local (in Ireland at any rate) and the less processed the product, generally the lower our water footprint will be.


    1. Paul Mella. Irish Water plan on using reed beds to treat waste. Irish Independent. 10/9/2014.

    This article first appeared on the website of Feasta – the Irish Foundation for the Economics of Sustainability

    Féidhlim Harty is an environmental consultant and writer, and director of FH Wetland Systems Ltd., a company specialising in wetland and reed bed design, willow systems and habitat enhancement. He is the author of Septic Tank Options & Alternatives and Permaculture Guide to Reed Beds, both published by Permanent Publications.

    The views expressed in our blog are those of the author and not necessarily lowimpact.org's

    1 Comment

    • 1Tim September 5th, 2023

      Feidhlim Harty book

      http://www.wetlandsystems.ie/watertips.html is wurth reading.

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