Water Resources in Hong Kong 

Resources
Introduction
Water Cycle
Water Resources in Hong Kong
Water Conservation
Climate Change

Index

Foreword
Acknowledgement
References
Rivers@HK Database

Lee, Frederick and Lee, Angela (2024) ‘Water Resources in Hong Kong, in Lee, Frederick. (ed) Water Resources Information Portal. Hong Kong: Centre for Water Technology and Policy, The University of Hong Kong.

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water-cycle

1. Local water resources

Introduction

According to the 2021/22 Annual Report of the Water Supplies Department, 18% of Hong Kong’s total water supply came from local rainfall, 23% were seawater used for flushing, and 59% were water imported from Dongjiang.
Rainfall in Hong Kong

The average annual rainfall in Hong Kong, for the period of 1981-2023, was 2,400 mm. Of the total annual precipitation, 85% were recorded between April and September each year.

According to the Hong Kong Observatory, there is a projected increase in rainfall for the period of 2081-2100, compared to the 1995-2004 average annual rainfall figure of 2,456 mm.

Based on an analysis of scenario data provided by the Intergovernmental Panel on Climate Change, calculations suggest a 4.7% increase under the high emission scenario (Shared Socioeconomic Pathways, SSP 3-7.0), and a 9.0% upswing under the very high emission scenario (SSP 5-8.5).

Local yield refers to rainwater that is captured by water gathering grounds.

Water gathering grounds

Water gathering grounds are land areas that have been set aside to collect rainwater. Rainwater gathered by streams and catchwaters within the water gathering grounds is conveyed to impounding reservoirs for storage.

Water gathering grounds cover approximately one-third of the city’s total land area.

Most water gathering grounds overlap with Country Parks, which are protected by the Country Parks Ordinance.

Rivers

There are over 200 natural rivers and streams in Hong Kong. The majority of them, however, are short and unnamed.

In Hong Kong, most natural rivers are situated within water gathering grounds. The city’s steep and rugged topography, together with our warm and humid climate, facilitates weathering and soil erosion, ultimately giving rise to the formation of river channels.

Rivers alter the configuration of river channels when they flow downstream.

River channels can be demarcated into three sections: the upper course, the middle course, and the lower course. Each section has experienced distinctive fluvial processes, resulting in the formation of unique landforms.

Moving water shapes the land surface by fluvial erosion and creates a network of channels. Fluvial erosion occurs in three directions:

  1. Headward erosion: River erodes in an upstream direction, lengthening the river channel.
  2. Lateral erosion: River erodes laterally, widening the river channel.
  3. Vertical erosion: River erodes downwards, deepening the river channel.

There are four types of fluvial erosion:

  1. Hydraulic action: The shearing force of the water hits the river banks, causing rocks and sediments to crack and break apart.
  2. Abrasion: Materials carried by the river wear away river banks and bed.
  3. Attrition: Rocks carried by the river collide with each other and are broken into smaller and rounder rock particles.
  4. Solution: Soluble parts of rocks and sediments are dissolved in the river.

The upper course of a river is usually located uphill, featuring a steep gradient and a small river discharge. Major landforms include interlocking spurs, plunge pools, and waterfalls.

The middle course has a gentle gradient and a medium discharge level, with major landforms including meanders.

The lower course is characterised by a very gentle slope and a large discharge, with a major landform being the floodplain.

For more details, please click here.

In Hong Kong, rivers are typically short and lack a middle course. Most natural rivers in Hong Kong are not “perennial streams” that flow throughout the year. Instead, many are “intermittent streams”, flowing only during the wet season, or “ephemeral streams”, responding to rainfall.

Rivers and streams play a crucial ecological role and serve as vital habitats for diverse plant and animal life. In Hong Kong, rivers are home to over 190 species of freshwater fish and 20 species of frogs.

Recognising their high ecological value, the Agriculture, Fisheries and Conservation Department has designated 33 natural streams and rivers as Ecologically Important Streams.

Preserving these habitats is essential to maintaining biodiversity health.

For more details, please click here.

No, not all rivers in Hong Kong are natural.

Some natural river channels, originating from or passing through urban areas, have been significantly altered and transformed into concrete-lined drainage ditches.

These extensively modified drainage channels are referred to as urban channels (or urban rivers) and were known as “nullahs” in the past.

The streamflow of some rivers is intercepted by man-made water intake points. The intercepted water is then diverted to reservoirs via catchwaters.

Shenzhen River is the longest river in Hong Kong. It is a border river demarcating the boundary between Hong Kong and Shenzhen.

Major rivers in Hong Kong include: Kam Tin River, Lam Tsuen River, Ng Tung River, Shan Pui River, Sheung Yue River, Shing Mun River, Tuen Mun River and Tung Chung River.

Reservoirs

There are two major categories: Impounding reservoirs and irrigation reservoirs.

Impounding reservoirs Capacity (mcm)
01 High Island Reservoir 281.124
02 Plover Cove Reservoir 229.729
03 Shek Pik Reservoir 24.461
04 Tai Lam Chung Reservoir 20.490
05 Shing Mun Reservoir 13.279
06 Tai Tam Tuk Reservoir 6.047
07 Lower Shing Mun Reservoir 4.299
08 Kowloon Reservoir 1.578
09 Tai Tam Upper Reservoir 1.490
10 Kowloon Byewash Reservoir 0.800
11 Aberdeen Upper Reservoir 0.733
12 Tai Tam Intermediate Reservoir 0.686
13 Aberdeen Lower Reservoir 0.486
14 Shek Lei Pui Reservoir 0.374
15 Pok Fu Lam Reservoir 0.233
16 Kowloon Reception Reservoir 0.121
17 Tai Tam Byewash Reservoir 0.080
Irrigation reservoirs
01 Hok Tau Irrigation Reserviors
02 Lau Shui Heung Irrigation Reservoir
03 Tsing Tam Upper Irrigation Reservoir
04 Tsing Tam Lower Irrigation Reservoir
05 Ho Pui Irrigation Reservoir
06 Wong Nai Tun Irrigation Reservoir
07 Hung Shui Hang Irrigation Reservoir
08 Lam Tei Irrigation Reservoir
09 Shap Long Irrigation Reservoir

There are 17 in-use impounding reservoirs. In addition, there are one obsolete impounding reservoir (Wong Nai Chung Reservoir) and nine obsolete irrigation reservoirs.

Impounding reservoirs store rain water collected by water gathering grounds; some of them also store imported freshwater from Dongjiang.

The overall storage capacity of the 17 impounding reservoirs in Hong Kong is 586.05 million cubic meters (mcm).

High Island Reservoir, the largest, has a storage capacity of 281 mcm, while Tai Tam Byewash Reservoir, the smallest, has a storage capacity of 0.08 mcm.

A majority of the reservoirs are located within a natural drainage basin. In addition to collecting rainwater from its natural basin, supplementary catchwaters have been constructed to divert rainwater from adjacent natural basins to the reservoirs, thereby increasing the amount of water entering the reservoirs. The catchment areas lying outside of the reservoir’s natural drainage basins are also known as “indirect catchment areas.”

For example, a nine-kilometer-long catchwater system was built to connect several basins outside of the catchment of Shing Mun Reservoir. This system connects several adjacent catchments—such as Ha Fa Hang, Sheung Fa Hang, Pak Shek Kiu Hang, Ngau Liu Hang, Tai Tso Stream, and Tai Yuen Stream—to Shing Mun Reservoir.

This supplementary catchwater system facilitates the capture of additional rain water to be stored in Shing Mun Reservoir, beyond the amount captured by its direct catchment area.

Irrigation reservoirs are no longer operational because the demand for irrigation water has dropped precipitously since the 1970s. A significant decline in agricultural activities and a drastic reduction in the size of farmlands due to urban development have rendered the function of irrigation reservoirs obsolete.

There is no need for concern if the dried-up reservoir bed belongs to reservoirs such as Lower Shing Mun Reservoir, Tai Tam Intermediate Reservoir, and Tai Tam Tuk Reservoir. These reservoirs serve a flood management purpose; they were built to hold excess water that overflows from higher-elevation reservoirs. It is normal for them to have lower water levels or be empty in the drier months.

In addition, irrigation reservoirs, such as Lau Shui Heung Reservoir, were originally designed to supply water for agricultural use, not potable use. Since they do not store water for potable use, there is no need for concern if they record lower water levels or are empty in the drier months.

2. Dongjiang (East River)

Introduction

Population and economic growth in the post-war period outpaced the capacity of local water gathering grounds to meet Hong Kong’s growing water demand. Since 1965, Hong Kong has supplemented its locally captured freshwater by importing water from Dongjiang (East River). In 2021-22, water imported from Dongjiang constituted 59% of Hong Kong’s total water supply.
Dongjiang river basin

Dongjiang is the eastern tributary of the Pearl River. It originates in Xunwu county, Jiangxi Province, and flows in a southwesterly direction through Guangdong Province.

Hong Kong needed to import freshwater since the 1960s because local yield was not sufficient to meet growing water demand.

Hong Kong has been importing freshwater from Dongjiang since 1965.

In the upstream zone: Ganzhou in Jiangxi Province, and the northern parts of Heyuan and Meizhou in Guangdong Province.

In the midstream zone: Heyuan, Shaoguan, and the northern and eastern parts of Huizhou in Guangdong Province.

In the downstream zone: Huizhou, Guangzhou, Dongguan and Shenzhen.

While Hong Kong lies outside of the Dongjiang river basin, it draws water from the downstream zone of Dongjiang through an inter-basin transfer scheme.

One upstream city (Meizhou), three midstream cities (Heyuan, Huizhou, and Shaoguan), three downstream cities (Dongguan, Guangzhou, and Shenzhen), and one city located outside the Dongjiang basin (Hong Kong) draw water from Dongjiang.

Dongjiang provides freshwater supply to more than 40 million people in these eight cities.

There is a very low probability that Hong Kong’s water supply would be interrupted in the drier years. The water abstraction ratio of Dongjiang is considered acceptable, with a 2021 reported long-term value of 27%.

The combined storage capacity of the three largest reservoirs in the Dongjiang river basin is sufficiently abundant to allow Guangdong’s water managers to perform one critical task: To control the release of water from these reservoirs, in times of drought, to ensure the river’s volumetric flow rate would reach a level that could satisfy downstream cities’ water demand.

Despite experiencing drier years, such as in 2021 when the rainfall amount in Dongjiang was 17.1% lowered than that of the previous year, Hong Kong’s freshwater supply has remained unaffected.

No, there are no increasing levels of competition for water among Dongjiang basin cities because the overall demand for freshwater in the basin has already peaked in 2011. The peaking is attributed to a reduction in water demand caused by diminishing agricultural activities in Guangzhou and Heyuan, as well as a drop in industrial activities across most cities in the river basin. The increase in freshwater demand due to population growth has been offset by a reduction in freshwater consumption that results from economic restructuring.

Dongshen Water Supply System

Rainfall collected by water gathering grounds in the Dongjiang river basin converges into the river’s main stem and flows along it towards the estuary.

Upon abstraction from a water intake point located in Dongguang, Dongjiang water is pumped uphill through four pumping stations (Taiyuan, Lianhu, Qiling, and Jinhu) to reach Shenzhen Reservoir.

The water is then conveyed by a pipeline to cross the border to reach the Muk Wu Pumping Station in Hong Kong.

Much energy is used to operate the transfer system’s pumping stations to enable Dongjiang water to reach Hong Kong.

After reaching Muk Wu Pumping Station in Hong Kong, Dongjiang water is conveyed to three reservoirs, or is shipped directly to water treatment works.

On the Eastern Route, Dongjiang water is shipped to Plover Cove Reservoir and High Island Reservoir for storage.

On the Central Route, water is shipped to Yau Kom Tau Water Treatment Works, Tai Po Water Treatment Works and Sha Tin Water Treatment Works for treatment.

On the Western Route, water is either shipped to Ngau Tam Mei Water Treatment Works and Au Tau Water Treatment Works for treatment or conveyed to Tai Lam Chung Reservoir for storage.

Three reservoirs—High Island Reservoir, Plover Cove Reservoir and Tai Lam Chung Reservoir—receive and store Dongjiang water.

Since 2003, a dedicated aqueduct has been utilised to convey Dongjiang water to Hong Kong to ensure its quality is kept up to specified standards.

The conveyance of Dongjiang water begins at Taiyuan Pumping Station. The water then flows to Shenzhen Reservoir via a dedicated aqueduct.

Imported water from Dongjiang undergoes treatment at water treatment plants in Hong Kong before it is supplied to users, complying with the city’s potable water standards.

Hong Kong Water Supply Agreement

As per the 2020 Hong Kong Water Supply Agreement with Guangdong Province, the annual guaranteed supply ceiling of water imported from Dongjiang is 820 million cubic meters.

According to the 2008 Dongjiang Water Allocation Plan, Hong Kong has been alloted a maximum of 1,100 million cubic meters of Dongjiang water and can request this amount if needed.

In 2021, the annual ceiling water price for 820 million cubic meters of Dongjiang water was $4,856.6 million. On average, the cost of raw Dongjiang water was $5.92 per cubic meter.

Since the actual amount of water imported from Dongjiang in 2021 was 811 million cubic meters (which was lower than the guaranteed ceiling amount), the effective cost of raw Dongjiang water was $5.99 per cubic meter in that year.

The purchased but unused water will not be imported into Hong Kong from Dongjiang.

Since 2020, a rebate mechanism has been incorporated into the Water Supply Agreement with Guangdong.

In each year, Hong Kong would make an upfront payment for 820 million cubic meters of water. According to the terms of the rebate mechanism, Hong Kong would receive approximately $0.3 per for each cubic meter of un-claimed water.

For instance, by the end of 2021, only 811 million cubic meters were imported into Hong Kong from Dongjiang, leaving 9 million cubic meters unused. As such, the total rebate amount was equivalent to $2.7 million (calculated as $0.3 x 9,000,000). This amount was deducted from the 2022 payment, reducing the latter from $4,950.51 million to $4,947.81 million, which works out to be a 0.05% discount.

The amount of imported water we have used in the past 30 years has varied year by year, with an overall average annual growth rate of 0.99%.

3. Is Hong Kong a water-scarce city?

Introduction

Hong Kong has enjoyed un-interruppted water supply since 1982. We anticipate the situation will coutinue into the foreseeable future.
Water provision in Hong Kong: Current situation and future considerations

In terms of volumetric availability of tap water supply, Hong Kong is not a water-scarce city. In fact, based on this criterion, Hong Kong is a water-abundant city.

According to the 2008 Dongjiang Water Allocation Plan, in drier years, Hong Kong could import up to 1,100 million cubic meters of water. When this figure is combined with the lower bound figures of local yield, the allocated quantity under the Dongjiang Water Allocation Plan would help ensure Hong Kong has an abundant (i.e., more than sufficient) supply of freshwater.

Moreover, the completion, in January 2024, of a water diversion project that conveys water from the Xijiang (West River) to the Dongjiang river basin has further augmented Hong Kong’s overall freshwater supply. This project allows for the diversion of up to 1.7 billion cubic meters of water annually from the Xijiang to meet the water demand of three cities located inside the Dongjiang river basin, such as Guangzhou, Dongguan and Shenzhen. Project proponents say that it includes a provision of emergency supply of water to Hong Kong.

The chance is very low.

According to the Hong Kong Observatory, projections based on IPCC data suggest that there is a likelihood of increased rainfall in Hong Kong in the long term (refer to Question 1.2).

Calculations based on multiple climate change scenarios have also projected increased rainfall levels in Southern China.

Water rationing was last imposed in Hong Kong in 1981. Since then, municipal water supply has never been interrupted.

Desalination

Desalination makes use of the reverse osmosis technology to transform seawater into desalinated freshwater. Reverse osmosis refers to a process of applying pressure to seawater to push it through a semi-permeable membrance. Salt and impurities are removed, yielding freshwater as a product.

The first stage of the Tseung Kwan O Desalination Plant was commissioned in December 2023.

The plant will go into full operational mode to produce freshwater when needed.

The first stage desalination plant can produce up to 50 mcm of fresh water each year.

As per a document presented to the Legislative Council by the Development Bureau, dated 2012, the proposed capacity of the desalination plant was determined to be 50 mcm. This figure was equivalent to 22% (upper bound) and 49% (lower bound) of the annual local yield for the period of 2001-2010.

According to data provided by WSD, the costs of water provision, on a per cubic meter basis at 2023 price level, were as follows:

Rainwater: HK$5
Dongjiang water: HK$11
Reclaimed water for non-potable use: HK$9.8 (March 2012 estimate)
Desalinated seawater: HK$13.5

Rainwater is the cheapest source of water. While the costs of Dongjiang water and reclaimed water are higher than rainwater, they are cheaper than desalinated water.

No, desalination is not a necessary option, based on an analysis of Hong Kong’s current water supply situation.

First, Hong Kong benefits from an abundant freshwater supply, sourced from the Dongjiang, at lower costs than desalination, even in drier years. In addition, Xijiang has become, since January 2024, a reliable backup source of freshwater for Hong Kong.

Moreover, while we should explore all possible solutions to capture sufficient freshwater to meet the needs of people now and in the future, we should also strive to reduce the adverse impacts of water use on the climate system.

Desalination, as a highly energy-intensive technology, would exacerbate climate change because it would generate much greenhouse gases emissions. The adoption of this technology should therefore be minimised as much as possible.

Hong Kong should, instead, formulate alternative, low cost, low carbon strategies to manage our water resources in a sustainable manner. The proven methods include water loss control, use of reclaimed water and water conservation, which can substantially lower the overall level of total demand for freshwater.

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