Well, I decided to do a quick search on the concept of Water Washing and why anyone would or should do it. There's actually a website fully dedicated to it - Water Only Hair Washing. Yes, WOHW is an acronym, one that I had never seen before (Can there be a hair care dictionary already?)
There is allowance for clarifying the hair every other month (or even longer), but it's suggested that you use only natural shampoos.
The main thing that gives me interest in this method of natural hair care is that you don't need any products at all! So it's definitely pocket-friendly. You still of course need to detangle your hair often (weekly I think).
The lady who started this method says she has been doing it for over a year and is very happy with her results.