The brewer at a local brewery is adament that "if your water tastes good to drink don't mess with it"
That is such unfortunate advice. There really isn't anything further from the truth in brewing.
I invite you to read Nov/Dec 2015 issue of Zymurgy where really simple water adjustments are presented. No math or programs, just a few simple doses of one thing or another to help brewers determine if their beer got better (or worse) based on their perceptions from their previous batches and new batches.
The only truism that can be created from that brewer's statement is: If the water tastes bad, you can't brew with it.
Good tasting water is important, but it doesn't guarantee good beer. Even the old timers knew that there were things they had to do to create decent beer. The problem is that our non-apprenticed brewing education doesn't impart the wisdom that was developed through generations of brewing experience. While those rules and procedures that were developed in previous centuries may not make sense to us now, they were found to be necessary through trial and error.
The other thing to remember is that just a few hundred years ago, local was the only beer there was and you made whatever beer you could make based on your local conditions and ingredients. The successful brewers devised the local rules and procedures that produced their best local beer. That means that they brewed a narrow range of styles. If brewers want to brew more than the style of beer that is well-suited for their local water, you do have to perform adjustments to your water.