I also used tap water for many years but the change to RO/DI was the best thing I ever did. No more fighting algaes, cloudy water, changes in the tank when the local treatment plant changed their chemical dosages and pH etc. I now have total control over my water quality.
The biggest issue with tap water is you have zero control over its quality and it can change at any time with no notice. Even though it may leave the deep well or treatment plant as "potable water" what is to say Joe Contractor doesn't dig into the water main up the street from you and cause a backflow incident when the sewer main 4 feet away gets washed out? Or when the neighbor next door fertilized his garden and has his hose laying in a pool of water and it gets sucked back in? You have no control over what happens and the water utility is not at fault since the water was drinking water quality when it left their facility. I have dozens of photos and stories documenting all of these instances and more from my 40 years in the municipal water industry and most are not pretty. It happens every day all over the world. A RO/DI costs about $125 and is extremely cheap insurance against all of this. We worry and fret about lighting, live rock, substrate, the glass our tank is built out of but none matters if your water is high quality.