I know that filtering 'clean' water using straw was done in Africa only a few decades back. What I don't know is whether that was only part of the process or not - but Grandma swears by a hot cup of tea, so I suspect the straw was to remove anything solid and boiling dealt with microbes etc.
Reed-beds are well-established sewage treatment system provided winters are not hard enough to freeze the system for weeks
http://www.wte-ltd.co.uk/reed_bed_sewage_treatment.html