2 cups Water (pre-boiled)
3 TBS lemon juice
1 TBS vinegar
UPDATE:Okay here is the buzz on this. I like this window cleaner - but I don't love it. Yet. After having used commercial window cleaner for so long - this one seems to take more effort to use - mostly because it stays wet on the surface for longer. (thus longer wiping time) I've done a bit of research on this one and a lot of sites say to add a TBS of rubbing alcohol. The alcohol will evaporate quickly causing the spray to dry faster and require less polishing time.
I'll update again if I decide to try that :)
If you make your own cleaners - I'd love to hear about it!