My understanding is that this water needs to be produced, that is taken from a source, processed, cleaned, pumped into pipes, etc. It means that you eventually

My understanding is that this water needs to be produced, that is taken from a source, processed, cleaned, pumped into pipes, etc. It means that you eventually have to divert and dry up rivers, lakes, or underground reserves to produce the water. This can destroy ecosystems because they're not getting the water anymore. It is possible to use more water than comes it and thus empty the buffer. The other issue is that it displaces water. For example, California has a water problem. Most of the water used to grow vegetables is then shipped away in the produce to far away where they're consumed: the water will never make it back to California. It puts even more strain on an already tapped out water supply. Finally, used water becomes polluted. Some chemicals are very hard to remove from water (some fertilizers, antibiotics, antidepressants...) and so the water is not exactly as it was, it's degraded.