The simple answer is that we ...

The simple answer is that we are not connecting one source of water to another source of water.

What is being connected are two or more ecological and chemical systems, which may or may not be complementary.

For instance, starting with the term "water".

Water for a chemist has a very different meaning than plain H2O. I'm just quoting one source for understanding this. This would include the minerals, dissolved or undissolved picked up by the river during its journey.

For instance, rivers flowing from the Himalayan regions have traces of placer gold in them. As examples, this interesting paper based on an old document of the 14th century, and a more recent 2015 news item about a GSI report on the Subarnarekha river in Jharkand.

Personally aware of this because of my interaction with the GSI as the India representative of an Australian airborne mineral surveying company in 1989.

Similarly different rivers would be carrying minerals from the regions they flow through.

Next microbial and biological organisms. For instance the incidence of schistosomiasis increased when the Aswan High Dam was made in Egypt. For more you can refer to this article .

Then the piscine population and other aquatic organisms. Will they be complementary, or will one destroy the other.

Therefore unless the effects of each of these factors are known, linking riverine systems can be disastrous.

Politicians do not think before making pronouncements, and neither do officials working under them produce unbiased reports .

Let the matter be studied by knowledgeable people, not connected with the government , before deciding on the linking.