Relooking at the numbers of Singapore's water supply: 3 very interesting deductions (part 1)

In preparation for my talk on Water Security and Safety & its Economics for Future of Singapore forum (you can also hop over there to see a short write-up of what we have discussed), I was looking (and relooking) through some of our official numbers regarding SG's water supply. No surprise here, the above forum was partly organised in response to the recent announcement by the government to jack up the price of tap water by 30% over 2 years. (I said "partly" because the forum is one in a long series of forums in education, energy, food security - all talking about the future of good, old SG.)


The thing I like about attending discussion, forum, dialogue (in contrast to lecture, rally, monologue) is the free flow of ideas among the participants. Even though I was the speaker at the forum, I have learned lots from everyone there. It proves that one does not have to be a professional/expert in an area to participate. Insights can be obtained from anyone, young or old, as long as he is willing to think critically and share his thoughts. In fact, after some valuable feedback from the audience, I relooked (again) the numbers to come up with new nuggets of knowledge.


Here goes...
(Updated by author: I have reworked the numbers because I mistakenly used US gallon instead of imperial gallon for PUB's figures. Nevertheless, the conclusion remains the same in its meaning. Henceforth, "gallon" refers to Imperial gallon whenever it is presented.)


I love rainwater!


Nothing new to readers of this blog. I have been advocating rainwater harvesting (RWH) as a source of fresh water, especially for rural locations or in developing countries. But here, I am applying RWH to an entire country - SG.


Some known facts

1. SG's water demand = 430MGD (Imperial mega gallons per day) (PUB)
2. Land area in SG = 710km2
3. 2/3 of land area constitutes our water catchment, channelling the rainwater into our 17 reservoirs (PUB)
4. Annual rainfall in SG. Depends on which literature source you are reading, it can hit a maximum of 2.4m/yr or a low of 1.1m/yr in 1997. Let's use last year's (2016) value of 2.0m/yr. (Data)
5. 2017 Newater contribution to water supply = 40% (PUB)
6. 2017 desalination's contribution to water supply = 25% (PUB)
7. Updated by author: (ST, 10 Jul 2016) "The Separation Agreement, which formalised Singapore's independence after it separated from Malaysia in 1965, guarantees us the right to extract 250 million imperial gallons a day (mgd) of raw water from the Johor River. This right expires in 2061." This works out to about 58% of 430MGD.

Based on 2/3 land area for catchment and 2016 rainfall record of 2.0m, we can theoretically collect....
...
...
...
a whopping 570MGD!!!

1. Wow!!! We have enough rainwater to more than satisfy our total demand of 430MGD!!!
2. Admittedly, there are losses of rainwater from the sky to the land, then to the reservoirs e.g. evaporation, infiltration into the ground, absorption by plants. (Fortunately (or unfortunately), we do not have that much forested or gardened areas left for infiltration and plant uptake.)
3. Whatever, rainwater that  makes up 130% of our entire country's water demand is not something to be sneered at.
4. On a side note, we are indeed blessed to have an abundance of rainwater compared to say, Australia or the Middle East.
5. Strangely, there are no statistics on the breakdown on the % contributions of local catchment and imported water (from Malaysia). But let's assume reasonably that we can do without imported water now so local catchment can contribute the remaining 35%. Keep in mind that this means our Newater and desalination plants are all working at full capacity which have implications in terms of maintenance and cost.
6. Anyway, 35% contribution from local catchment --> 150MGD ONLY
7. Why are our reservoirs currently collecting 150MGD when we could have collected 570MGD?
   ......
   ...
8. (Btw, the above blank spaces are supposed to be a hint for you to start thinking.) The answer in one word is STORAGE. We simply do not have enough space in our reservoirs currently to keep all this rainwater!
9. But all is not lost... I will list some possible solutions in a later post.
10. IF we can fully harvest and store all our rainwater, what roles do Newater and desalination have to play? Will they still be as prominent?

For your ease of reading, I will continue on to the other deduction(s) in the next post. Ciao.

Figure: My favourite reservoir - MacRitchie. Despite using the latest technologies in Newater and desalination, the use of reservoirs for rainwater harvesting should be retained and in fact RWH should be augmented to fully capitalise on our abundant rainfall.

Singapore latest water attraction - Sengkang Floating Wetland

I finally had the chance to visit this latest water attraction in Singapore. It is not in Sentosa but right in the middle of Punggol Reservoir surrounded by Sengkang, Anchorvale and Punggol housing estates. Publicised since at least 2007, the Sengkang Floating Wetland was finally launched in Nov 2010 by PUB (Public Utilities Board). See PUB press release 07 Nov 2010: Wet and Wild

Figure: PUB poster on "Sengkang Floating Island" (circa 2007)

Figure: A map showing the floating wetland (in green) in the middle of Punggol Reservoir with Anchorvale Community Club in the east and Sengkang Riverside Park in the west

What I found highly useful are the numerous signboards describing the wetland, how it works, the importance of the watershed (covering Punggol, Anchorvale and Sengkang) and the various water plants grown on the wetland itself.

Figure: This is probably the best take-home message from the signboards. It actually shows the delineation of the watersheds (light blue)for all 17 reservoirs (dark blue) in Singapore. Of particular interest are the white areas which represent non-watershed areas i.e. rainwater falling in these areas do not go into any reservoir. A good guess would be about 70% of Singapore's land area is used to collect rainwater. Another interesting point is Changi Airport area is NOT a watershed though the airport itself harvest rainwater for its own water demands. See previous post - How to reduce flooding in Singapore? Harvest more rainwater!

Now, a floating wetland is a kind of constructed wetland but unlike the traditional constructed wetland, it floats on the surface of a water body rather than acts as a container for the water body. Flotation is achieved using a mat of polymeric material which acts as a substrate for water plants to grow and at the same allows the roots to penetrate into the water column. PUB already has several of these floating wetlands (in a smaller scale) in other reservoirs - Lower Seletar, Pandan.
(Update: Sengkang Wetland is based on BioHaven floating islands which have been used in other countries.)

Figure: A mini floating wetland at Pandan Reservoir

Figure: A conventional constructed wetland in Mississippi (http://coastal.msstate.edu/cwres.html)

Constructed (and floating) wetlands are usually designed to clean up the water, improving water quality. The roots and the underside of the polymeric mat tend to accumulate a layer of biofilm containing bacteria, fungi and algae which help in the decomposition of organic matter, nitrogen (e.g. ammonia) and phosphorus compounds. The water plants themselves also can absorb nitrogen and phosphorus, as well as certain heavy metals. Their roots extend into the water column not just for aesthetics but they can also filter and trap sediments. Such a use of plants to clean up the environment is known as phytoremediation. For a more complete discussion, check out this post - Before you write off a plant as a weed, read this

Besides the benefits of cleaning up water and providing a refuge for wildlife, a floating wetland has several advantages over a conventional constructed wetland. It is easily fabricated elsewhere and several units can be joined together to make a large wetland in actual deployment. It can be conveniently placed in existing water bodies without excavation and retrofitting of the existing landscape. If you find lake X has poor water quality, just push a few floating units into the lake. And when they have accomplished their tasks or if problems crop up, they can be conveniently removed as if they were never there in the first place.

However, a key design of constructed is the depth and width of the water body. For the plants (and associated biofilm) to work their magic, the water has to pass through the zone of influence of the roots. A lone floating wetland in the middle of a wide and deep river is not likely to have enough juice to clean up the river. I am not sure how deep the Punggol Reservoir is but if it is like most reservoirs, probably a few metres deep. I doubt the roots can reach to such depths. Also, when I look at the map of the Sengkang Floating
Wetland (see above), it appears exactly like a lonesome patch of greenery surrounded by a swath of blue. Can it really improve the water quality? If yes, how much? (As a side note, I may be conducting water quality monitoring workshops here so perhaps, the water quality data can provide a better picture.)

Anyway, water cleaning efficiency aside, Sengkang Floating Wetland is an excellent showcase of Singapore's focus on active, beautiful and clean water.

Figure: A boardwalk connects the floating wetland to the 2 banks and allows visitors to get up close and personal.

Figure: Viewing the floating wetland and boardwalk from Anchorvale CC. Notice Sengkang flats in the distance

Phytoremediation of Wastewater

Hi Chen Ko,


Hope all is well with you. While researching on phytoremediation for wastewater, I chanced upon your blog.
http://waterqualityinsingapore.blogspot.com/2010/03/before-you-write-off-plant-as-weed-read.html

Your blog has enhanced my understanding of phytoremediation and its potential in SEA. In the blog, you mentioned Earthship Biotecture. Do you happen to know the company/inventor behind this concept?

Thanks.
Best Regards
I


Hi I,

Glad to hear that you find my post useful. From what I know, Earthship Biotecture was founded by Michael Reynolds. The idea of an Earthship is a self-contained living environment that maximises the recycling of water - closing the loop as they call it, and minimises the wastage of energy. Food is actually a "by-product" of the recycling of water. Though it does not mean 100% self-sustaining as in a spaceship, the concept is nevertheless useful as a model for future housing.

If you are seriously interested in Earthship, you can actually sign up at the website as a volunteer to help out in the construction of their current projects. Unfortunately, there are no projects in our region as they are mostly located in the U.S.

Or if you prefer to find out more before diving head-first into the physical work, check out the 2 books by Michael Reynolds.

1. Earthship
2. Water from the sky

Here is a review of book #2 that I have written for my campus library in 2007.


Do you want to harvest rainwater and recycle your wastewater so that you will never have to depend on public utilities? Perhaps you simply want to reduce your rising water bills. Or perhaps you are an environmentalist at heart and feel strongly about conserving such a vital resource like water. If you have any of the above goals, this book excels in illustrating the processes of rainwater collection and recycling of both grey and black water. Detailed designs are available for the reader to immerse into the bolts and nuts from choosing the right materials to building a functional system which includes water treatment for rainwater, grey water and black water. Numerous photos and illustrations enable the reader to visualise each stage of the construction. This is however not a science book since the scientific reasons behind most designs are not well explained. The reader is advised to find out more about the science from other sources. One major shortcoming is the lack of costing details, impeding the reader from gauging how economical such a system is. Even though the author claims that the recycled water is drinkable after treatment, there is no mention of any physical, chemical or microbiological test being done. The relevant tests would have strongly validated his claims. Despite the above inadequacies, the book presents plenty of useful hands-on information that many “scientific” books lack. It should be read by anyone interested in rainwater collection and wastewater recycling.

How to reduce flooding in Singapore? Harvest more rainwater!

Harvesting of rainwater may sound foreign to most of us even though this term is commonly used in other countries. It simply means collection and storage of rainwater. It may be on an individual, residential, community or even national basis.

Actually, Singapore has been harvesting rainwater for a long time on a national basis. From PUB's webpage, two-thirds of the land area here is available for rainwater catchment (Yes, right, "catchment" is more commonly used here).

(Figure: www.pub.gov.sg/water/Pages/LocalCatchment.aspx)

Is so much of our area covered by reservoirs? NO! It means that land (residential, industrial, recreational, waste etc.) is used to funnel all that rainwater into reservoirs. For example, rainwater falls on rooftops, flows into drains which lead into canals, ultimately joining up with a reservoir. Because of the flash floods in June, everyone now knows that Orchard Road is part of the catchment area for the Marina Reservoir. Talk about practical environmental education.

Indeed a very clever system to alleviate the shortage of water in this densely populated island. However, it suffers from a few drawbacks.

One, in times of heavy rainfall, no way will the reservoirs be able to hold so much water. The natural thing to do is to drain the excess into the sea. (E.g. the Marina Barrage is well touted to be able to do this in the event of heavy rains.) This of course means a waste of fresh water. AND IF the excess CANNOT be drained (e.g. blockage of some water way), flooding will result. In the (good?) old days when Singapore is still a tropical jungle, most rainwater will be soaked up by the vegetation and soil. But with the increase of built-up area, we no longer have such a luxury. Most rainwater will flow over the ground surface straight into drains and canals or perhaps accumulate in some low lying area as a flood.

Another challenge of open reservoirs like ours is the loss of water through evaporation. In the dry months, the water level in the reservoirs drops not only because of the lack of rainfall but also through the above mentioned loss.

This article predicts that the rainwater harvesting (RWH) markets in Europe and India are set to experience high growth rates in the coming years due to a rising fresh water shortage. More RWH systems will be installed at the residential, commercial and industrial levels.

Guess what? This is nothing new in Singapore! Changi Airport has such a system. Nanyang Polytechnic has one too. The airport is reported to satisfy one-third of its water demands in this manner, saving $390 000 per year. Such water is normally collected on the roof-top and undergoes minimal treatment for non-portable use e.g. toilet flushing, firefighting drills, watering of plants.

Imagine... if we have more of such systems, not only will our reservoirs be less stressed in times of heavy rain, there will also be less loss of precious fresh water through evaporation.

If your interest has been piqued, how do you set up a RWH system. SIF Technologies is selling a "chemical free RWH system". Chemicals are sometimes added in conventional water storage to discourage microbial growth. (Chlorine in PUB water does this job.) In the case of SIF, they are using a proprietary non-chemical means to do the same thing.

But RWH can be simple and cheap. Consider this 3rd world method of RWH. However, remember to always discard the first 10min of so of rainwater as it may contain pollutants from the air or your roof-top.

Figure: using a tin roof to collect rainwater (Water for Life, Hesperian Foundation)

Figure: My own version of a RWH system for use in a high-rise flat from a project several years back. (Naturally, we can't have every household in a HDB block harvesting rainwater. I suspect only the top floors will get any significant amount. The other concern is not to have a high-rise RWH system becoming killer litter.)

Oh, before you rush out to install a RWH system, here is an extract from Singapore Law.

SEWERAGE AND DRAINAGE ACT

PART V PROTECTION OF WATER RESOURCES
Prohibition on extraction of water
No person shall, without the approval of the Board (PUB), construct any works for taking or intercepting water from any place or sea, within the territorial limits of Singapore.

However, I believe the law has been relaxed for residential installation provided the storage tank is less than a size of 5x2x2m. Anyting bigger will require a water-borne fee to be paid. But if you are planning a system for your company or school, you still have to go through the bureaucracy for permission. One last point, check out the guidelines for collection of rainwater at NEA.

(Update: Rainwater Harvesting Seen as Solution for Drought and Flood Control: In Kenyan cities like Nairobi, rainwater harvesting is seen as a solution to multiple problems.)