What is this “water technology” actually; what does it (not) include?

The sector Water Technology is large, in the sense that it covers a broad variety of subjects. It deals with technology making sure that are drinking water is safe to technology that makes wastewater safe to flow back into nature. Thus, dealing with clean fresh-water. Other technologies focus on the climate change, such as the shortage of clean fresh water, how to create fresh water from salt water and to do this in a durable way (not using a lot of energy and/ or chemicals for instance). But, there is more, how can you make use of salt to fresh water by getting energy out of it? How can we recycle nutrients from water?
What is not part of Water Technology are for instance subjects like how to build defensive structures (e.g. dikes) against rising water, of course this is technology and has to do with water, however is part of civil technology.