This is absolutely not correct. We can handle the minerals, fluoride and chlorine/chloramines and in fact without the chlorine we could become quite ill from dozens of issues. Fluoride - there are many plants that react quite badly from such as spider plants, dracaena, orchids, peace Lily, and there is a long list of these sensitive plants. The vast majority of plants don’t like either chemical. Some can tolerate it better without noticeable symptoms but they won’t ever develop to their prime capacity of growth.If its safe for your to drink, I can't see it harming plants.
And getting rid of chlorine/chloramines is not as easy as setting a bucket out in the sunshine anymore. You could do that 40-50 years before chloramines became necessary due to potential leaks in our aging water grid and main supply system of our systems and even the ever increasing disease pressure that makes it more important that the water is as safe as possible. Also, for people who fill bottles of water and let it sit for months just in case the water supply is cut off — you can think chloramines for helping that water stay safe for a longer period of time. Chloramines are much more stable and is active much longer— it can’t be broken down by a shallow container of water sitting in the sun and being agitated to release the chlorine gases over a period of 24-72 hours. 40-50 years ago, when I raised tropical fish (angels and bettas) and had 6 big tanks in my home — I filled large galvanized tubs and put fish oxygenator pumps in them so the agitation could go on day and night. Then I ran it through all kinds of filtering material and then boiled on the stove before cooling and putting back in the tank. I put it in closeable buckets and boiled it right before needing it for twnk changes or top offs. If you just sat a narrow top bucket out in the sun (3-5 gallon) and didn’t agitate the water — it takes much longer for the chlorine to evaporate. However, today with chloramines it’s a different ballgame. All municipalities now use (chlorine and a type of ammonia) which keeps it from breaking down and letting us get sick — you can sit a container out in your yard and it might be 2-3 weeks plus to reduce the levels. You can buy a good quality set of chlorine test strips to see where your post levels are and then after 24 hours, 36 hours,etc. Don’t buy the cheapest you can get. That’s the only way to be sure water from any RO system or so called inline hose filters is operating. Same with using a TDS meter when seeing if your RO system is removing the minerals it needs to so you can more effectively fertilize your potted plants, or those used with hydroponics. It’s not that plants don’t want the minerals, just the opposite. They critically need NPK (nitrogen, phosphorus and potassium) along with secondary of calcium and magnesium, and the micronutrients/minerals but they need them in the right amounts and correct ratios. So you start with 0 and add what is needed. Or you test your water for hardness, pH, and use a fertilizer appropriate. You do this by sending a sample to somewhere like JR Peters Laboratory (who develops many different types of plant fertilizers (commercial). Meaning they know plants — any water lab can test your water and give you the numbers. But these labs aren’t horticulturally or agriculturally trained or based to know what types of plants or crops you grow need. Someone like JR Peters - they test your water (well, municipality tap, spring, pond, etc etc ) and can advise what to do to make it safe for the plants, and useable in determining the best plant growth using that particular water — this includes but isn’t limited to the best type of fertilizer that works with that crop. If you are using fertilizer meant to be used with pure water and you are using tap water at various pH levels and various levels of minerals - you are behind the 8 ball. Same with plants that need way more potassium like hibiscus and you are using a Klite fertilizer (potassium light or not existent in the mix). Our world would better shape and people would have more money in their pockets and they would be happier with their results if they just tested their water sources and their soil. Soil tests is critical — you can’t really tell what you have if it’s not scientifically tested. Oh you can guess if your hydrangeas are deep purple that you have highly acidic soil (4-4.5) or that if pretty pink - the soil is more alkaline with a pH close to neutral or slightly above ie. 6.5-7.2 maybe a smidge higher. If your lawn soil is 4.5 — you won’t have pretty grass. And if it’s not getting calcium and magnesium along with appropriate levels of nitrogen — it’s not going to be healthy. You can fertilize til the cows come home but without proper pH you are throwing money out the window. And stop killing your clover — it fixes nitrogen in the soil to where you don’t need as much nitrogen fertilizer. Believe me it works. If you don’t like the size of white dutch clover or the blooms sticking up — use the specialty micro clovers.
now I know we are talking about aquatic plants but if it’s sensitive to fluoride and chlorine/chloramines— then no you don’t want to just use tap water just because you don’t keel over from drinking it. If you have a well that needs frequent heavy chlorine shocking - you might have an issue too. It’s the same issue if you are adding fish to the fountain, aquatic garden, etc.They will not be happy in water that’s not the appropriate pH and then has all this fluoride and chloramines in it which can reduce their health and end up killing them.