Technical Report Draft 2

This proposal has been developed in response to the request for proposals on developing solutions to an engineering problem.

Water demand in Singapore uses approximately 430 million gallons a day. 45% of water usage is consumed by the domestic sector and the non-domestic sector takes up the rest. Singapore’s water supply is obtained from four water sources known as the Four National Taps. The Four National Taps consist of local water catchment, NEWater, desalinated water and Malaysia imported water. Local water catchment, NEWater and desalinated water contribute 40% of the water source, while Malaysia imported water contributes 60% of the water source. These water sources has helped with meeting the increase in water demand. According to Public Utilities Board (PUB) (2018), Singapore’s water demand is expected to double by 2060, with the non-domestic sector using about 70%. With the increase in demand of water usage, water prices are expected to increase gradually. Therefore, to keep up with the water demand in Singapore, planning and implementation of water saving strategy is required.

The geographical location of Singapore is located near the equator which results in higher precipitation. Based on figure 1, Singapore’s rainfall intensity is increasing over the years.

Figure 1: Annual Rainfall Total in Singapore (1980 - 2017)

As Singapore has high rainfall intensity, the practice of stormwater management is essential. Stormwater management is the control of surface runoff. As Singapore becomes more urbanised, there will be an exponential increase in surface runoff. Urban Redevelopment Authority states that the projected distribution by 2030, about 79% of the land in Singapore will be filled with infrastructure (Urban Redevelopment Authority, 2010).

Due to rapid urbanization in Singapore, more high rise buildings and infrastructure were being built which leads to the increase of surface runoff on rooftops. Therefore the implementation of rainwater harvesting on rooftop is regarded as a prefered method in Singapore context.

An ideal forward-looking campus should adopt implementation of rainwater harvesting on rooftop so as to be self sustainable and reduce dependency on external water sources. Nevertheless, rainwater harvesting has not been implemented in the new SIT@punggol. Without the implementation of rainwater harvesting, the reliance on using external water sources will increase the incurred cost of water. Having the SIT@Punggol campus planning committee adopt rainwater harvesting process, external water usage will be reduced and the campus would be self-sustained with the water supply.

The purpose of this report is to propose that the planning committee of SIT@Punggol campus to adopt rainwater harvesting on rooftop of the new campus to reduce the usage of water from external source so as to be self-sustainable.

We propose to implement rainwater harvesting system within SIT@Punggol compound. Rainwater harvesting will reduce water consumption from external sources. In addition, it promotes the school towards being self-sustained. 

Rooftops are the main area where rainwater will be collected. The slope of the roof affects the rate of water runoff. Argilife (n.d.). As the roof gets steeper, the faster the rate of water runoff. A less-steep or flatter room will increase the chances of water contamination to stay on the water catchment surface as water moves more slowly. Therefore, we recommend the building to have a steeper rooftop (see Figure 2) to maximize the rate of water runoff to increase the amount of water collected. 

Figure 2 : Rainwater Harvesting System

Gutters will be placed at the side of the roofs (see Figure 2.1) for the collection of rainwater from the roof surface runoff. The gutters will also act as an medium for the water to flow into the pipes and into the storage tank.

Figure 2.1: Gutter installed at the side of the roof (climateTechWiki)

According to PUB requirements, vertical physical air gap of at least 150mm is required between the potable water discharge point and the top of the rainwater collection. The air gap is to ensure no risk of contamination into the potable water supply. 

Collected rainwater will be transport by the pipes into the rainwater collection tank. The rainwater collection tank shall be mosquito proof to prevent chances of mosquito breeding. NEA (2011). Storage tanks should be located as close to supply and demand points and be protected from direct sunlight. Overflowing pipes must be installed in the top tank to allow the safe disposal of excess rainwater and to prevent flooding. 

Through effective filtration and retention measures via ABC Waters design features, runoff from the site can be treated to remove pollutants and silt, thereby protecting the water quality.Ultrafiltration (UF) membranes, UV disinfection and controlled chlorine are some of the method used to provides residual disinfection after the water leaves the storage system. UF membranes is a separation process using membranes with pore sizes in the range of  0.1 to 0.001 micron to remove remove high molecular-weight substances.Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses short-wavelength ultraviolet (UV-C) light to kill or inactivate microorganisms Hypochlorous acid (HClO) is a weak acid that forms when chlorine dissolves in water, and is very proficient at killing bacteria such as salmonella and E. coli.

There is a need to ensure treated rainwater is free from bacterial and safe for reuse.
Water are treated by treatment plant that is engineered to meet the similar standard as the National Sanitation Foundation (NSF)
and American National Standards Institute (ANSI) Class A System. The Class A systems are designed to disinfect
and remove microorganisms including bacterial and viruses.

Case Study 1 (United World College)

Case Study 2 (Hwa Chong Institution Student Facility Block)

The school wanted to harvest rainwater and stormwater for irrigation and toilet flushing.
The integration of rain and stormwater harvesting system, irrigation system, water treatment system and the
featured vertical rain forest is the primary challenge of this project.