Perfect tense-Have/Had?

the perfect is used to indicate an action occurred earlier than the present time often focusing attention on the resulting state rather than on the occurrence itself.

An example of a perfect construction is given by the English sentence I have made the dinner – although this gives information about a prior action of making the dinner, the focus is likely to be on the present consequences of that action (the fact that the dinner is now ready). The word perfect in this sense means "completed"

Here in this context, "reservoirs and water treatment plants have been constructed" means they were constructed in the recent time.

Where as had been constructed is totally wrong. Do you know why, the past perfect should be followed another past occurrence. When I reached the station, the train had already left.

Without referring a past incident we never use past perfect.