Atch’s Weblog

We all know that 75% of the Earth’s surface is water. But do you know that of the 500,000 cubic kilometres of rainfall each year, only 20% falls over the land, and only 1% of that is stored and useable for us?

If you think water is renewable – yes, you are right. But do not think there is a never-ending supply.

Have you ever thought about how much water goes down the drain each time we take a shower, do the laundry, water our garden, wash our car, or just wash our hands quickly? In a typical household, more than 1,000 litres of water is used in a day, and at least 60% of that can be reclaimed for use elsewhere because it is not totally “black”, it is just “grey”. Let me explain.

In construction terminology, the water coming into our houses is thought of in terms of clean, “white” water, and that going out from our toilet is known as “black” water. So, “grey” water is somewhere between. By most definitions, grey water is tap water soiled by our use in washing machines, bath tubs, showers and hand-basins. It’s not sanitary, but it’s also not toxic and generally disease free. Black water is produced after flushing the toilet as it contains harmful bacteria and disease-causing pathogens which cannot be used for domestic irrigation like on a lawn.

What separates white from grey are the types and concentration of additives caused by our washing, bathing, cooking and cleaning. Therefore, grey water may contain soap particles, fat and oil from cooking, hair and even flakes of human skin.

A typical house has at least three water systems. The first one is used for white water distribution, the second for grey, the last for black. Only the first comes into the house and the last two go to the sewer, but with special treatments.

Grey water normally passes filtration for solid waste then goes directly to the city sewer. Black water must go through the water treatment system (i.e. septic tank) to ensure it contains no pathogens before being discharged to the city sewer.

However, if the grey water coming from your kitchen contains too much fat and oil, it is advisable to send it to the oil filtration and treatment system also.

From all this, you can find an opportunity to reduce the consumption of white water, not only to reduce your water bill, but also to help conserve the environment. One good example is to not use drinking water to flush toilets or on your garden. Grey water can be used to feed plants in your garden as it contains nutrients such as nitrogen, phosphorous, and potassium, the basic ingredients in fertiliser, which can sustain plant life and recharge topsoil. However, some substances found in soap such as sodium, chlorine and boron will cause problems for plant life. If you are going to use grey water for your garden, start looking at what you send down the drain.

You can keep chemical contamination to a minimum by using environmentally friendly, biodegradable soaps and detergents whenever possible.

Also, for soap, using high-phosphate brands will harm your plants as they can only live within a limited level of phosphorous concentration.

Some may wonder how to collect grey water? And how can you feed your plants? First of all, your house must have separated waste water pipes; one for grey and the other for black. The grey water pipe is commonly known as the waste pipe, whereas the black water pipe is called the soil pipe. Second, if grey water is in good condition for plants, you need a water tank equipped with a filter. Try to estimate the quantity of grey water use daily so that you do not have it left in the tank.

If you have more grey water than you need for your garden, simply let it go to the city sewer. To prevent contamination, do not store it for too long as it will turn into black water within 24 hours after bacteria in the tank start to grow.

You might face some problems with clogging in the filters and pumps due to bits of hair, skin and food. Remember that chemical clog removers are harsh and can seriously harm not only your plants but also anybody in contact with the garden such as pets and kids. Natural solutions, such as boiling water or vinegar and baking soda treatments might be less damaging to plant life.

Lastly, what kind of plants can be fed with grey water?

Fruit and vegetable plots are best irrigated with white water or rain water, so it is recommended that you prevent grey water from coming into contact with such plants due to the contamination risk, especially if the produce will be consumed raw. Consider using grey water for plants with some distance between them and the food.

All these “Feeding Green with Grey” suggestions might be difficult at first. But if we realise that we have the potential to reduce a large amount of our household water consumption by recycling all this grey water, it is quite a sound measure to reduce the impact on the environment. There are still plenty of ways to live “green” without having to grow more trees.

ผู้ช่วยศาสตราจารย์ ดร.อรรจน์ เศรษฐบุตร

Asst. Professor Dr. Atch Sreshthaputra

Faculty of Architecture, Chulalongkorn University

Chairman of Green Building Program. The Association of Siamese Architects.

           Human can survive a week without food. However, only two or three days without water can lead to fatality. So, water is the most precious resource on earth, but why is it the most misused, abused, and misallocated natural resource? By the numbers, one person drinks 1-2 liters of water per day, but spends 100 liters for outdoor activities like gardening, cleaning, and entertaining. In 70 percent of worldwide water use that is allocated to farming; most of these farming irrigation systems operate at only 40 percent efficiency.

            There are a lot more about statistics that makes us feel a bit guilty with living our daily life; not to mention about the number of people who have to live in parts of the world where it rains only once every 10 years. Luckily, Thai people have chosen the right location on earth to live without having to fight for water; until recently that we have experienced water shortage in the Eastern Seaboard. There was a fight between local people and factories over water in Rayong two years ago. Most people are not aware that this travel destination would have water shortage. Building design and construction in this region then need to incorporate features that can contain the situation. But what is it?

            Last year, one of my architecture students proposed the use of very large water tanks on the rooftop of his high-rise residential project in Rayong. He thought it could reserve enough water throughout the dry season if the water shortage occurs. However, he insisted on having a private swimming pool at the balcony of each living unit just because this is a travel destination; people go there for spa!!! Sadly enough, he refused to provide a water retention pond and more green area on site as he needed some space for outdoor parking!!! He said it is difficult to find enough water to maintain the green area; and an empty water retention pond will look really nasty!!! He also said that he has to trade a higher cost of construction due to the weight of water for his building to not having to face the water shortage. He went on talking about another benefit of the rooftop water tank in terms of solar heat protection, which is not the point here. I must say that teaching this young generation makes me learn many things about how people today perceive environmental crisis differently. I can not say that his reasoning is totally incorrect, but it is not quite right to me.

            So what goes wrong with his idea? And why we should have green area or water pond in our houses. Imagine the land without our houses built on; when it rains, storm water will find its way down underneath through pervious surfaces, filling up the groundwater, and the rest will flow to natural water channels. That is the way nature works since the beginning of time. As soon as we move in to occupy the land, we replace the existing green area with the houses built with concrete. We replace natural vegetated surfaces with impervious concrete slab used for parking our cars.

            There is no doubt why storm water cannot be recharged into ground water, thus causing water shortage in the long run. To make the matter worse, excess storm water which cannot seep through concrete slab will lead to a higher water runoff rate. It will fill up public sewers very quickly causing flooding right after severe thunderstorms. Here, you can imagine all the dirtiness we throw into the sewers will then overflow back on our streets, our backyards, or even our living room!! . I used to see all kinds of living creatures trying to evacuate from water-filled sewers. They are thousands of cockroaches, rats, snakes, or even DRAGONS. Of course, ecosystems also exist in the sewer!!!

            Now you get an idea why impervious concrete pavement can lead to serious effect on not only flooding, but also water shortage thereafter. I once said that green buildings are not only about planting more trees in the buildings. However, covering all your open space with hardscape and not providing enough water reservoirs will be worse than you could imagine; especially if everyone else is doing the same as you do. This is why housing developers are forced by government to build retention ponds so that the complex will not discharge water to the public sewage system too quickly. Some are forced to retain its storm water for at least three hours after a thunderstorm. All this regulation is built upon a concept that new housing development should not discharge more storm water than is the empty site used to before development.

            To ‘Green’ your water means much more than to ‘Clean’ your (waste) water to a maximum BOD allowance (i.e., Biochemical Oxygen Demand) as it is all about landscape design, planting, retention pond, and pervious green area where storm water can penetrate through easily. New innovative product known as ‘turf pave’ or pavement which allows water penetration will help ‘green’ our water as it could sustain load from vehicles while allowing storm water penetration. This product seems to answer all the questions related to my student’s project in Rayong. We will see this kind or products coming to the market more and more in the near future. Let’s cross our fingers if it will become widely available soon before people start to fight for a drop of water.

ผู้ช่วยศาสตราจารย์ ดร. อรรจน์ เศรษฐบุตร

Asst. Professor Dr. Atch Sreshthaputra

Faculty of Architecture, Chulalongkorn University

Chairman of Green Building Program. The Association of Siamese Architects.