I have quite a lot of lime in my water supply, so I use it 1:200 in distilled water (mostly 120 Acros, Rollei or Foma). Not a trace of a spot on any of my negatives, so I won't reuse it. The fact that I load two 120 films on a spool helps with the economy of developing, but that's the only corner I'm willing to cut. (50% savings is a lot, anything else is just not worth it)