a RO unit will take your tapwater ppm from your present 040, to about 002 (at least, mine does) ... most importantly, it will remove the chlorine from a city water supply ... chlorine will NOT harm your plants, but it will kill beneficial bacteria that do help your plants ... BUT, then you will have to add CalMag+ to make up for the removed calcium, magnesium, iron, etc... ... it's a 'cost' decision for most people ... :jointsmile: