There is absolutely no deabte to even have, because tap water is different depending on where you're at, and even which house you live in. Every American has a right to a FREE water quality report upon request to the water company. Get a report on your water, and then post the results. Nobody on this board can say tap is good for your tank, simply because it depends on the tap it comes from. Even the best tap has silicate trouble and this causes diatoms.....basically tap makes a tank way harder to keep clean and beautiful......we would need a report from your water company to give any thoughts as to your quality.....tap is not tap....it's different everywhere. RO/DI will make your hobby life MUCH easier, but you may be able to get by on tap depending on the report......even then....water companies flush their systems with chemicals on certain days.....do you know which days?