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.

*Problem Solution*

How water is Collected

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 (Allegiance)

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.

How it is being transported

PUB requirements

Base on the PUB requirements, there must be a Vertical physical air gap of at least 150mm shall be provided between the potable water discharge point and the top of the rainwater collection tank to ensure no risk of contamination to the potable water supply. Additionally, the owner shall ensure that the rainwater collection system is designed with a bypass system to allow rainwater to be directly channeled into any drains or watercourses, upon any direction issued pursuant.

First Flush Diverter- The first flush of water from the roof can contain amounts of bacteria,

Instead of flowing to the water tank, these pollutants are diverted with the initial flow of water into the chamber of the water diverter

Figure 3: First Flush Diverter(roof filter)

How it’s being filtered

Due to unusual molecular structure, water have a amazingly good at dissolving things, thus in order to have pure water to drink or use, the water must be filtered properly. Water filters uses two different methods to remove dirt from the water. The two different techniques are physical filtration and chemical filtration. Physical filtration means straining the water to remove larger impurities while chemical filtration involved in passing water through an active material that remove the impurities chemically as it pass through.

There are four main types of filtration that uses physical and chemical techniques. The four main types are activated carbon, reverse osmosis, ion exchange and distillation.

By using activated carbon, chemical impurities can be draw out and trap in the charcoal through a process called adsorption.

In reverse osmosis process, contaminated water is being force through a

How it’s being stored

The rainwater collection tank shall be mosquito proof in accordance to the “Guidelines on Mosquito Prevention in Domestic Rainwater Collection System for Non-potable Uses". A copy of the Guidelines is available on NEA website

Storage tanks should be located as close to supply and demand points as possible and should be protected from direct sunlight.

Overflow pipes must be installed in the top of the tank to allow the safe disposal of excess rainwater and to prevent flooding

Excess rainwater shall be discharged into a watercourse or other collection medium and not allowed to be discharged into the public sewer. in accordance to the allowable discharge limits stipulated in Singapore Standard SS593: Code of Practice for Pollution Control.

How it’s being treated

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)

http://www.netatech.com.sg/index-4_6.html

https://www.nsf.org/newsroom_pdf/water_55_insert.pdf

Case Study 2 (Hwa Chong Institution Student Facility Block)

http://www.netatech.com.sg/index-4_7.html

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.

How it’s being used