Where Does Hong Kong's Drinking Water Come From?

Hong Kong is known for its efficient water supply system, but it faces unique challenges due to its geographical limitations. The city's annual water consumption is substantial, according to statistics from Hong Kong University (HKU), stating that Hong Kong consumed a total of 1,376 million cubic meters (mcm) [of water] in 2021, comprising 1,055 mcm of freshwater and 321 mcm of seawater.

Global Ranking of Water Consumption

While Hong Kong's total water consumption is significant, its per capita consumption is relatively high compared to some Asian cities but lower than many Western cities. For instance, in 2021 according to HKU, Hong Kong's per capita daily domestic freshwater consumption was about 280 liters, which is higher than major Asian cities like Tokyo.

All the below information comes courtesy of the Water Supplies Department of Hong Kong.

1. Pok Fu Lam Reservoir - 170,000 cubic meters of water
2. Aberdeen Lower Reservoir - 190,000 cubic meters of water
3. Aberdeen Upper Reservoir - 455,000 cubic meters of water
4. Tai Tam Byewash Reservoir - 47,000 cubic meters of water
5. Tai Tam Intermediate Reservoir -152,000 cubic meters of water
6. Tai Tam Tuk Reservoir - 4,693,000 cubic meters of water
7. Tai Tam Upper Reservoir - 764,000 cubic meters of water
8. Shek Pik Reservoir - 12,805,000 cubic meters of water
9. Kowloon Byewash Reservoir - 449,0005 cubic meters of water
10. Kowloon Reservoir - 562,0003 cubic meters of water
11. Shek Lei Pui Reservoir - 305,000 cubic meters of water
12. Lower Shing Mun Reservoir - 750,000 cubic meters of water
13. Kowloon Reception Reservoir - 117,000 cubic meters of water
14. Shing Mun Reservoir - 10,085,000 cubic meters of water
15. Tai Lam Chung Reservoir - 13,260,000 cubic meters of water
16. Plover Cove Reservoir - 131,689,000 cubic meters of water
17. High Island Reservoir - 197,598,000

TOTAL: 374,091,000 cubic meters of drinking water (maximum capacity) across all impounding reservoirs in Hong Kong.

There are three main sources of drinking water in Hong Kong. These are:

1. Rainwater: Rainwater accounts for about 18% of Hong Kong's drinking water. In Hong Kong, approximatelyone-third of the land area is designated as "Water Gathering Grounds," which play a crucial role in collecting rainwater. Most of these water gathering grounds overlap with Country Parks, which cover about 40% of Hong Kong's land area.
2. Dongjiang River Water (Since 1965): Imported from Guangdong Province, this accounts for about 70-80% of Hong Kong's freshwater supply. The Dongjiang River is actually a tributary of the Pearl River, which flows through China's Jiangxi and Guangdong Provinces.
3. Desalination: The Tseung Kwan O Desalination Plant, commissioned in December 2023, adds to the freshwater supply by producing up to 50 million cubic meters annually. Desalination can make up about 5% of Hong Kong's freshwater supply. Desalination is the process of removing the salt content from sea water to make it drinkable.

Step 1: Collection of Raw Water

• Source: Raw water is collected from impounding reservoirs
• Process: Rainwater collected in Hong Kong's reservoirs and Dongjiang water imported through pipelines are the primary sources of raw water.

Step 2: Transfer to Water Treatment Works

• Infrastructure: Large transfer mains and tunnels transport raw water from reservoirs and Dongjiang to water treatment works.
• Location: These transfer mains and tunnels are located underground and sometimes cross the harbor via submarine pipelines to reach treatment facilities across Hong Kong.

Step 3: Water Treatment

• Process: At the water treatment works, raw water undergoes several treatment stages:
  
  1. Pre-treatment: Chemicals are added to coagulate particles.
  2. Clarification: Large particles and impurities are removed in clarifiers.
  3. Filtration: Finer particles are filtered out using gravity or biological filtration.
  4. Disinfection: Water is disinfected to kill bacteria and viruses.
  5. Fluoridation: Fluoride is added for dental health benefits.

• Facilities: There are now 21 water treatment works in Hong Kong with a total output capacity of 4.8 million cubic metres per day.

Step 4: Storage in Service Reservoirs

• Infrastructure: Treated water is pumped through large trunk mains or tunnels to service reservoirs.
• Location: Service reservoirs are typically located on high ground to utilize gravity for water distribution.
• Function: These reservoirs provide transient storage to manage peak demand and maintain supply pressure.

Step 5: Distribution to Buildings

• Infrastructure: Water flows by gravity from service reservoirs through the distribution network, which includes over 8,400 kilometers of water mains.
• Location: Water mains are located both above and below ground, stretching across urban and rural areas.
• Delivery: Water reaches the connection point at the lot boundary, where it enters the building's internal plumbing system.

Step 6: Internal Plumbing System

• Components: The internal system includes a sump tank, roof tank, pipes, and fittings.
• Maintenance: The Water Supplies Department maintains pipes up to the lot boundary, while property owners or management agents are responsible for the internal plumbing.

Step 7: Final Delivery to Taps

• Outcome: Water is delivered to the taps of residential, commercial, and industrial buildings across Hong Kong.

Additional Details

• Separate Systems: The freshwater supply system is completely separate from the seawater supply system used for flushing toilets.
• Reliability: Hong Kong's water supply system is highly reliable, covering 99.99% of the population with continuous quality water supply.

According to Hong Kong's Water Supplies Department (WSD), the city's tap water is treated to meet the World Health Organization’s Guidelines for Drinking Water, as of 2017. Regular checks are performed to make sure all water supplied meets these stringent standards.

However, it is always best to boil your water from the tap since the facilities of each apartment building can be different. The WSD advises that you can drink tap water provided that your building “carries out proper upkeep procedures including regular cleansing of water storage tanks…and frequent monitoring of water quality to maintain the original water quality standard.”

Hong Kong is a pioneer in using seawater for flushing toilets since the late 1950s, driven by the need to conserve freshwater resources. This innovative approach not only helps reduce the demand for freshwater but also contributes to environmental sustainability. Currently, about 85% of Hong Kong's population uses sea water for flushing.

Environmental Benefits

The use of seawater for flushing is environmentally friendly for several reasons:

• Conservation of Freshwater: By using seawater, Hong Kong conserves a significant amount of freshwater, which is essential for drinking, cooking, and other domestic purposes. This reduces the strain on freshwater resources, which are often limited and require extensive treatment processes.
• Reduced Carbon Footprint: The lower "electricity consumption for supplying seawater than fresh water, also reduces carbon dioxide emission. Consumers, furthermore, can reduce their water bills."
• Cost-Effective: Seawater is cheaper to treat and distribute than freshwater. "For 2020-21, the unit production cost of seawater was $4.2 per cubic metre as compared to that for fresh water of $9.8 per cubic metre."

Process and Infrastructure

The process of using seawater for flushing involves several key steps and infrastructure components:

1. Seawater Collection: Seawater is collected from seafront pumping stations located around Hong Kong's coastline. There are currently 42 pumping stations in operation.
2. Treatment: The collected seawater undergoes basic treatment, which includes screening to remove debris and disinfection with sodium hypochlorite to ensure it meets the Water Quality Objectives for Salt Water for Flushing Supply set by the Water Supplies Department (WSD).
3. Storage and Distribution: Treated seawater is stored in salt water service reservoirs before being distributed through a network of pipes to buildings. As of March 2021, there were 54 salt water service reservoirs and over 1,660 kilometers of salt water mains.
4. Dual Plumbing Systems: Since 1965, all new buildings in Hong Kong have been required to install dual plumbing systems to separate potable water from seawater used for flushing. This ensures that the two systems do not mix and that seawater does not contaminate freshwater supplies.

Since Hong Kong lacks large rivers or lakes of its own, it has to rely heavily on water supplies from China's Dongjiang River for its freshwater needs. This leads to some rather serious issues as Hong Kong's population grows and its water consumption rate increases.

Some issues include:

1. Unfavorable Agreements: Under Guangdong's "lump sum package deal," Hong Kong pays for a fixed water supply, regardless of actual consumption, resulting in wasted resources and costs (HK$4.5 billion wasted as of 2017).
2. Rising Water Costs: The price of imported water from Guangdong has doubled due to increased competition for water in the Pearl River Delta.
3. Depletion of Water Resources: Water from the Dongjiang River Basin has been depleted by 30% in the past decade due to booming populations in cities near the Pearl River Delta.
4. Water Wastage: A significant amount of water (32.5% of total production) is lost due to theft and leakage.
5. Underdeveloped Water Resources: Failure to switch to alternative water resources on a larger scale, like desalination and water recycling, has increased reliance on mainland water, from 22% in 1965 to 76% in 2012.
6. Worsening Dongjiang Pollution: Back in 2015, manufacturing facilities had dumped perfluorinated compounds (PFCs) into the Dongjiang river. According to Chan Hon-fai, who chairs the Water Supplies Department’s advisory committee on water resources and the quality of supplies, “We have conveyed our message to officials in China. Honestly, they have no knowledge of PFC and haven’t done anything yet.” Overreliance on a polluted freshwater source could be catastrophic is safety standards are not maintained.