However, treated water production figures are only given for Sg. Langat, Sg. Semenyih and two other minor plants. One noticeable omission is the production figures of Bukit Nanas treatment plant, which gets all its raw water from the Klang Dates dam.

The only reason provided by the authority for the omission is that there has been no water rationing in areas in Kuala Lumpur which are supplied by the Bukit Nanas treatment plant. However, since other details on the Klang Gates dam are given, and for better transparency, production figures for Bukit Nanas plant should also be included unless there is something to hide from the public.

Unlike Sg. Langat and Sg. Semenyih treatment plants, the production capacity of Bukit Nanas plant depends solely on the level of water in the Klang Gates dam. Water from the dam is conveyed by gravity via an approximately 10km long twin-pipeline to the treatment plant situated at Bukit Nanas. The treated water is then delivered to its supply areas also by gravity. When the dam is full at about 95m Ordinance Datum Level (ODL) the maximum rate of flow of water from the dam to the Bukit Nanas treatment plant is about 190 million liters per day (mld). Due to hydraulics, the flow rate is reduced to about 130 mld when the water level at the dam is at 89.5m ODL.

The other two treatment plants, Langat and Semenyih, are sited at more than 15km downstream from the dams. Normally they extract water from the rivers for treatment. During drier months when the amount of water in the rivers downstream of the dams is less than that required for treatment, water from the dams is released to supplement the river flows.

The above is the only difference in the operating procedure of the two types of dams for water supply purposes.

The safe yields of all these dams have been designed based on the estimate of a drought happening once in 30 years. In all cases, the dams are designed such that they can be recharged to the full by the end of each year. In the following year water is released from the dam to supply the treatment plant directly or to supplement river flows in the drier months of January to March and July to September as the case may be. Then in the wet months from October to December, the dams are recharged. This cycle goes on year after year without any trouble of water deficit unless a drought of severity worse than 1 in 30 years occurrence is encountered.

So far the authorities have not come out with any statement on the severity of the current drought. Therefore it is reasonable to assume that, if the current drought exceeds a return period of 30 years, all three dams should exhibit similar water-stressed phenomenon. But why is it that when water rationing is required in areas supplied by Langat and Sememyih treatment plants, those supplied by Bukit Nanas could get away without rationing?

May be the reason lies in the manner in which the dams are operated. In the case of Klang Gates dam, water is delivered "hydraulically" to the treatment plant and the amount depends solely on the water level at the dam. While at the other two dams, water is released as and when required to supplement the river flows and upon instructions from the operators of the treatment plants.

In other words, the operation of Klang Gates dam is not subject to elements of human judgement and errors; while that of the other two is. For Langat and Semenyih dams, water should only be released just enough for extraction at intake points and for maintaining compensation-flow downstream. May be the current shortage of water in these two dams could be due to lavish and wasteful releases of water from the dams.

The authority should seriously look into this matter; not turning it into a witch-hunt, but to prevent the recurrence of such a mistake, if there has been any in the operation of the Langat and Semenyih dams.