350 ppm does not mean your water is bad...you should fill a bucket and retest,chances are that it will go down about 20-30 ppm over night. Also, pull a report for your water (all water companies must provide them), it may be the ppm is coming from things you are gonna need like mag, calcium, silica, etc. You should know that if you use RO water you are going to have to supplement with all the additives you are going to remove in filtering, driving your ppm back up pretty close to where it was before.