What factors made beer so important to the establishment of civilisation?

I am guessing by the wording of the question that you saw or aware of the documentary "How Beer Saved the World". If you have not, the thesis of the documentary is that beer was integral to civilization on many different levels and even was it's genesis.

To be blunt I think it is a very poor documentary. It makes enormous jumps of logic that are very flimsy and is outright incorrect in many cases.

The question really should be "Why is alcohol so important to humans". Beer is just one way for humans to male ehtyl alcohol. Its a great way because grains are relatively inexpensive compared to grapes or honey and its available year round. In my opinion people drank alcohol during the time of the genesis of Civilization as they do now: because they like the psychoactive effects.

What made it a more practical drink than plane water?

It was not more practical than drinking water. Its basically a myth that people throughout history have had problematic access to water and thus were forced to drink alcohol instead. There is just no written or archaeological record to support this theory and it fails many basic logic tests.