I just completed the Fish River Canyon hike on the 24th of June. The water wasn’t as abundant as it was when I did it the first time round in late August 2010. I cannot recall that the river was “flowing” in either case.
The accounts of the water levels are very subjective. I encountered a group that finished the hike a day before us and they were recounting that they had gone very long stretches without water. I did not have the same experience.
We had pre-planned camping spots, but had to leave that idea behind because some of the sites did not have water. We however walked on/back to spots that had ample water.
As for water quality, the first time I did not bother with filtration or drops, but this time I had to support a couple of old folks and my wife, who did not appreciate water with texture. I used the Sawyer mini with a CNOC Vecto 2L bag (Amazon), but had to back flush every 2 liters to get back up to reasonable flow rates. This was my first experience filtering water, and I did not know how time consuming it can be with silty water sources. If I had to do it over, I would opt for a base camp gravity filtration setup, hand filtering 10 liters a night wasn’t enjoyable. If you are just looking after yourself, this is less of an issue. If you can tolerate the taste/texture, use drops, saves time which can be better used enjoying yourself.
If I were to do it in a month’s time, I would increase my water carry capacity to at least 3 liters (with the alerts of the low water levels, mine was already 4 liters) and fill up whenever I see a suitable water source. I would also not bargain on pre-planned camping spots having water and start looking for a camping spot a bit earlier at the end of the day.
I would however be on the lookout for other people’s accounts closer to your planned dates.