The webpage "Rainwater Harvesting 101" from Innovating Water Solutions LLC introduces what is rainwater harvesting is. Rainwater harvesting is the collection of run-off waters from buildings and other possible surfaces for future uses. In the past, rainwater used to be collected in gutters that channel water into storage units. However, rainwater harvesting can be as simple as collecting rainwater in a rain barrel or as complicated as a large cistern to supply an entire household in the modern times. The author believes that although the idea of rainwater harvesting conjures images of old farm cistern, the reality is that many countries are adopting this method because it has proved to be a viable method in supplying water. The author believed that rainwater harvesting is viable in the urban setting due to the convenience of collecting runoff water from roofs and directing it to a water storage tank. Hence, rainwater can help to supply water in a household.

In my opinion, having access to clean water is important in our daily lives to maintain our wellbeing; hence there is a need for Singapore to reduce the dependence on imported water and improve on other sources to get clean water. I believe that desalination of seawater is a better option to replacing imported water in the future than rainwater harvesting in Singapore.

Desalination is the process to make seawater into pure drinking water. Currently, Singapore currently has 5 desalination plant. SingSpring Desalination Plant produces 30 million gallons (Keppel Infrastructure Trust, n.d.), Tuaspring Desalination Plant produces 70 million gallons (Water Technology, 2015), Tuas Desalination Plant produces 24 million gallons (Jose, 2018), Jurong Island Desalination Plant produces 30 million gallons (ST Engineering, n.d.), and Keppel Marine East Desalination Plant produces 30 million gallons (Mohan, 2021), totalling to 184 million gallons a day. This makes up to 43% of the daily water consumption in Singapore, which is about 430 million gallons a day. This shows that desalination will make more contribution towards replacing imported water in the future in Singapore.

Rainwater harvesting in Singapore has progressed significantly since 2011. The water catchment area in Singapore has expanded from half of Singapore to two-thirds of Singapore with the expansion of Marina, Punggol and Serangoon Reservoir (PUB, 2023). According to Meteorologial Service Singapore (n.d.), the annual rainfall in Singapore has increased by an average of 67mm per decade using data from 1980-2019, hence showing the importance of rainwater harvesting. With a bigger catchment area to collect the increasing rainwater, rainwater harvesting’s contribution will increase as the years go by, making significant contribution to replacing imported water.

However, despite the contributions that rainwater harvesting can make towards replacing imported water, there is a flaw in rainwater harvesting in Singapore. With the growth of urban areas, there is limited space to expand the water catchment area. According to the Housing & Development Board (2021), Singapore has a big demand for housing from Singaporeans; hence HDB aims to build up to 23,000 Build-To-Order (BTO) flats per year in 2022 and 2023 to match the increase in demand. Singapore is a small country; hence this expansion will limit the area that Singapore has in expanding the local catchment area, stagnating the amount of water collected from rainwater harvesting. With these limitations in rainwater harvesting, it cannot be the major contributor to replacing imported water in Singapore as compared to desalination despite its contribution.

There is also one major drawback to desalination, which is the hefty cost to purify water. Since Singapore is relying on imported water to be the main source of freshwater supply, there is a need for Singapore to use desalination despite the major drawback of cost. Although PUB (Public Utilities Board) is currently using the reverse osmosis method that uses 3.5kWh/m3, Singapore is now exploring alternative methods to reduce energy consumption (PUB, 2023). Electro-deionisation is one of the methods that has been experimented and has achieved an energy consumption of 1.65kWh/m3 in a pilot plant (PUB, 2023). The energy consumption of this method is less than half of the energy used for the reverse osmosis method. Since this method proved to be more cost effective, PUB will be validating this method in the Tuas desalination plant (PUB, 2023). The con of desalination is not as significant because of PUB’s effort in experimenting different methods. With PUB’s effort in searching for alternative methods to purify water, desalination technology will advance, and the major flaw of cost efficiency will be compensated. Hence, desalination will be a bigger contributor to replacing imported water in the future than rainwater harvesting despite it contributing to replace imported water.

Although desalination and rainwater harvesting both have their pros and cons, desalination will be a better option to replace the reliance of imported water in the future due to these two reasons. Firstly, desalination has more consistency than rainwater harvesting. Rainwater harvesting requires rain for water to be collected while desalination requires seawater that is readily available. Lastly, comparing the cons of both desalination and rainwater harvesting, the cons of rainwater harvesting is more significant than the cons of desalination. There is more difficulty in improving the local catchment area in Singapore for rainwater harvesting due to the limited land space and ability to expand land in Singapore as compared to experimenting new methods for desalination. Despite the contribution that rainwater harvesting can bring to replacing imported water, it cannot be the biggest contributor as compared to desalination in replacing imported water due to the amount of water it can produce.

References

Housing & Development Board. (2021, December 16). HDB To Ramp up Flat Supply by 35% Over Next 2 Years.

https://www.hdb.gov.sg/about-us/news-and-publications/press-releases/16122021-HDB-to-Ramp-Up-Flat-Supply-by-35-Percent-Over-Next-Two-Years

Hong, J. (2018, June 28). Singapore opens third desalination plant in Tuas. The Straits Times.

https://www.straitstimes.com/singapore/environment/singapore-opens-third-desalination-plant-in-tuas

Keppel Infrastructure Trust. (n.d.). SingSpring desalination plant.

https://www.kepinfratrust.com/portfolio/environmental-services/singspring-desalination-plant/

Mohan, M. (2021, February 4). Singapore's first large-scale desalination plant capable of treating both seawater and freshwater opens. Channel News Asia.

https://www.channelnewsasia.com/singapore/keppel-marina-east-desalination-plant-pub-freshwater-seawater-303256

Maxwell-Gaines, C. (2020, July 27). Rainwater harvesting 101 | Your how-to collect Rainwater guide. Innovative Water Solutions LLC.

https://www.watercache.com/education/rainwater-harvesting-101

Meteorological Service Singapore. (n.d.). Weather Singapore.

http://www.weather.gov.sg/climate-past-climate-trends/

ST Engineering. (n.d.) News - Tuas Power-ST engineering consortium opens Singapore’s fifth desalination plant.

https://www.stengg.com/en/newsroom/news-releases/tuas-power-st-engineering-consortium-and-pub-open-singapore-s-fifth-desalination-plant/

Public Utilities Board. (2022, June 1st). PUB Desalination.

https://www.pub.gov.sg/watersupply/fournationaltaps/desalinatedwater

PUB. (2023, January 25th). PUB Local Catchment Water.

https://www.pub.gov.sg/watersupply/fournationaltaps/localcatchmentwater

HSL Constructor Pte Ltd. (n.d.) Tuas desalination plant 3.