Our country gets its water from various sources, 90% of the supply comes from rivers and streams. Nevertheless, all water resources are dependent on rainfall. Of the total average annual rainfall of about 320bcm for Peninsular Malaysia, 47% run off as surface flow and is available for use. The total annual water demand is estimated to reach about 14bcm by 2020 which equates to 12% of the total water availability. Dams are constructed along rivers to create reservoirs and water is drawn from these areas for water treatment plants throughout the country.
Groundwater accounts for 90 percent of the freshwater resources. The renewable water resources are 630 billion m3 (annual average water availability of about 28 400 m3 per capita). Based on this fact, Malaysia is a country with abundant water resources.
Table 1. Water resources in Malaysia
| Annual rainfall | 990 billion m3 (Ref 1) | |
| Surface runoff | 566 billion m3 | |
| Evapo-transpiration | 360 billion m3 | |
| Groundwater recharge | 64 billion m3 | |
| Surface artificial storage (dams) | 25 billion m3 (Ref 2) | |
| Groundwater storage (aquifers) | 5 000 billion m3 (Ref 3) | |
Water supply management and development in Malaysia is managed on a state-by-state basis; and to cater for the differences in supply and demand inter-state water transfer programmes have been implemented.
The Department of Environment (DOE) does the job of monitoring the river basins to determine the water quality in relation to major pollution sources. The Ministry of Health (MOH) is responsible for monitoring the raw water quality in the reservoirs at the intake points of the treatment plants. State Water Authorities or private companies then supply piped drinking water from the treatment plants to the population.
What is water catchment area?
It is defines as an area in which surface runoff collects and from which it is carried by a drainage system, as a river and its tributaries. Also known as catchment area; drainage area; feeding ground; gathering ground; hydrographic basin. (The Free Dictionary By Farlex)
It is an extent or area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean. In closed drainage basins the water converges to a single point inside the basin, known as a sink, which may be a permanent lake, dry lake, or a point where surface water is lost underground. The drainage basin includes both the streams and rivers that convey the water as well as the land surfaces from which water drains into those channels, and is separated from adjacent basins by a drainage divide. Other terms that are used to describe a drainage basin are catchment, catchment area, catchment basin, drainage area, river basin, water basin and watershed. (Wikipedia, The Free Encyclopedia)
A water catchment area
Ulu Langat Park
Kinabatangan River
Selangor State Park
Ulu Muda Forest Reserve
Table 2. Dams in Malaysia
| Single-purpose dams | ||
| Water supply | 34 | |
| Hydropower | 7 | |
| Irrigation | 3 | |
| Silt retention | 3 | |
| Subtotal | 47 | |
| Multipurpose dams | ||
| Water supply + Irrigation | 6 | |
| Water supply + Flood mitigation | 5 | |
| Water supply + Irrigation + Flood mitigation | 2 | |
| Hydropower + Flood mitigation | 2 | |
| Hydropower + Water supply | 1 | |
| Subtotal | 16 | |
Some of the water basins in our country
- The Main Range or Banjaran Titiwangsa - An important water catchment area for the whole of Peninsular Malaysia.
- Ulu Langat Park, Selangor-The forests of the Park are catchment for the upper reaches of the major rivers in Selangor (Sg. Bernam, Sg. Selangor, Sg. Klang and Sg. Langat). These river basins cover almost the entire state of Selangor. The Park is the origin of many smaller streams that merge to form larger rivers, including Sg. Kerling, Sg. Batang Klang, and Sg. Semenyih, that feed these major rivers.The Park area also feeds the 5 reservoirs (Sg. Selangor Dam in the Sg. Selangor river basin, Batu and Klang Gates Dams in the Sg. Klang river basin, Langat and Semenyih Dams in the Sg. Langat river basin). It provides 98% of the water supply to Selangor, KL and Putrajaya.
- Ulu Muda, Kedah- This last great piece of rainforest reserve spans 120,000 hectares and serves as a water catchment area for a major part of Kedah. Three great lakes are located in Ulu Muda - Tasik Pedu, Tasik Muda and Tasik Beris. The Ulu Muda forests also form the water catchment area for the Muda, Pedu and Ahning dams that supply water for drinking and irrigation to Kedah, Penang and Perlis.
- The Air Terjun Rive, Penang-The Penang Waterfall is within the water catchment area, vital to the supply needs of the island so it is closed to the public. Only10-15% of Penang water supply comes from this place. It has been one of historical sources of water for Georgetown and ships. In the first decade of the 1800s, the Waterfall was harnessed to supply water to Georgetown’s growing population. In 1805, an aqueduct was built from the Waterfall via Pulau Tikus to a reservoir near Leith Street Ghaut and Hutton Lane respectively (PBA, 1988).
- Batang Ai National Park, Sarawak- It is also the water catchment area to Sarawak's only artificial lake. This huge lake stretches up the Engkari and Ai valleys. The dam is part of the Batang Ai Hydro-Electricity Complex.
- The Padas River, and the Segama River, Sabah- Padas is the most important reserve in terms of future water supply in Sabah. It receives the most rainfall of above 4000mm annually, which is comparatively higher than other catchment areas in Sabah
- Tawau Hills Park, Sabah-It was gazetted to protect water catchment resources for Tawau Town and the Semporna Peninsula. At least 7 major rivers originate here. The Tawau River flows through the middle of the 27,972 ha park and forms many natural deepwater pools and waterfalls, for example, the Table Waterfall.
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