Using distilled/deionised water, combined with a wetting agent, for the final bath will give the best results. The streaks (assuming that you've properly washed the film) can be the water's mineral content, but they can also be attributed to too much, or too little wetting agent. A little experimentation will show how much is needed. Now, you don't need to freak out because of the streaks. For the vast majority of the cases, they're on the base side of the film and, IMHO, you don't need to rewash the film. I use a "wettex" (thin foil sponge), which I have washed well and keep clean. I roll a piece of it, wet it with water, squeeze it and wipe the streaks gently. The film will be dry within minutes and the streaks are gone. This only works when the streaks are on the base side, you'll need to rewash if they're on the emulsion side and, unfortunately, success isn't guaranteed. Streaking may or may not be seen on the prints/scans. Very light streaks don't show up in prints made with my condenser enlarger, at least when using normal contrast grades. Harder grades may reveal them but ,frankly, I couldn't care less.
PS Why is this thread in the "Medium Format" forum?