NO. R.O water isnt needed. and in my opinion, is more myth than fact as to the whys of using it impo. i use well water.
its pretty decent well water mind you, but well water non the less.
I PHd it Once when i started my 1st ever grow, to get an idea where it was. it was around 6.4, and ran about 300 ppm TDS. i didnt get a defined test to see what TDS percentages i have. atleast not since i put the well in 20 yrs ago.
you can use RO, but MN doenst RO her water, and most plant life seems to do just fine from MNs care.