CJB82
Boil water
Collect the steam in a condenser.
The steam condenses back to pretty pure water, while most of the impurities are left behind.
That's distilled water
As Kip mentioned - testing it for phosphates would be wise, along with other tests if you can.
If this "free" source of distilled water from your friend is unlimited ... I would use it for sure. Free is always good !
If it tests out good - no problem at all - as long as you are getting it in plastic jugs.