A cheaper alternative to an RO unit is a de-ioniser. I believe there are a couple available in the UK one goes by the name of 'Purity on Tap' I think. They are basically a long tube containing some medium (looks like fine dark coloured sand. You attach water via a hose at one end and the purged water comes out the other end. The rate must be kept slow though other wise it won't be completely cleansed, I think it takes roughly 15mins to fill a bucket. In the UK try animal house or Aquaitcs Direct as probably your cheapest source. Hope this helps, Ken.