Monday, April 17, 2017

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.

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