I heard that rain water is the best thing to use to water your plant. Someone told me it had to be clean thou, if i put some buckets outside and a window screen over them will that keep enough shit out or do i need to filter it better than that?
It depends really. Due to polution some rain water no longer has a neutral ph. With smog going into the clouds it causes ACID rain which can lower ph. You should test your rain water for ph and that will tell you. If you want ph neutral water just go with distilled.
You can get distilled water fairly cheap from any grocery store. I do not know if poland spring is distilled. i would assume it is spring water which would probably not have a neutral ph. spring water is usually high in dissolved solids. i am no expert but i would go with regular distilled water bought by the gallon or more if you can get a larger container. possibly 2 and a half gallons. just a suggestion. you can use tap water if you let it sit out for a week or so. letting it sit lets the chlorine evaporate. it would be cheaper than buying bottled water.
i would assume ro means reverse osmosis. i am sure it is expensive especially if you buy it from a nursery. reverse osmosis is a process where by use of pressure and a membrane water is pushed through a small membrane to remove solids from water. it is used to desalinate seawater. it is very effective at removing solids but once again it could be pricey. using a filter for tap water "brita filters" while not as effective would save money and be very easy to use.