Any people ever have leaking water from engines qnd various part after adding coolant? Is there truth that a system that had been using pipe water for too long will develop leaks after adding coolant? And the solution is to continue don't use coolant because it cause leaks?

Not sure whether the rusts were disturbed by the added coolant and thin out the metal. What leak isn't the radiator but the core plug (people call Water Jacket is a misnomer), it leak one by one after having added coolant. There are still some difficult to reach core plug which have not had been changed yet but seems to not leak for now but who knows if add in coolant it leaks again thats why was not keen to add coolant to it. Various mechanics said some myth about coolant being acidic and some said it would need very thorough flushing before adding coolant.

Acidic PH is usually theories on old unchanged coolant that have broken down in its chemical properties. But new coolant should be alkaline slightly or near neutral I read. But mechanic like to say it's acidic that's why it corroded your metal and call it a day. So don't put coolant if you haven't been using coolant since day one. That's their advice. Or risk the unknowns and leaks.