Your water contains a lot of calcium or magnesium dissolved in it. Distiller can take them out cheaply, filter equipment capable of doing this will require a much bigger init investment. A small RO filter unit will take out some, but not 100%. Check this out for more info, a home distiller will look like your outside ac unit. It does drain some water out (so not 100% efficient) http://www.purewaterinc.com/html/why_is_distillation_best_.htm