Best entails plants grown in tap water are not as good, which is false. All RO water is doing is giving you a neutral base to start, so you can meticulously control the amounts of every nutrient/micro-nutrient.
Tap water contains larger molecules of Ca and Mg for example that aren’t easily absorbed by roots and are not chelated so they may bind with other minerals, whereas the artificial CalMag we use is chelated and smaller molecules allowing it to efficiently absorb. Using a beneficial bacteria tea can actually help here by breaking down those larger molecules.
The perceived problem with high ppm water as a start is nutrient lockout. This isn’t a result of high ppm, but a result of pH fluctuations due to minerals/nutrients binding and causing pH swings. However, you do not need to worry about most minerals in tap binding with minerals from additives because the majority of hydroponic nutrient solutions are chelated which just means compacted to where they can’t bind with other molecules, the only molecules that will bind are the non-chelated ones, with beneficial bacteria tea can help with. Using tap water will require more frequent pH adjustments to avoid swings outside the optimal 6-7 range to avoid lockout of nutrients tho.
Chlorine in small amounts is not harmful to plants and chlorine is actually a micro-nutrient plants need to breakdown H20 and transport nutrients among other functions.You want to reduce the Chlorine by evaporating for a period of time (1-5 days) depending on the levels in the water, I just do 1 week. However, some water companies use Chloramines instead, this cannot be evaporated, but removed with carbon filters.
If you search around a bit you will find tons of people growing all kinds of plants to include cannabis, perfectly fine with great results using tap water. If you go to your water companies website, you can usually get the latest report and see what all is in the water. WardLabs is also a resource to use, you can mail in a water sample and they will run a full top to bottom report on it for you telling you every single thing in your water.