I've never heard of a humidifier leaking because of not using purified water.
Humidifiers that use ultrasonic elements to vaporize water can, as I understand it, get buildup from residue. You can get a white dust from them. But I wouldn't expect them to leak.
I've never had any issue with use of tap water in humidifiers. I've used the variety that just wicks water up into a material and has a fan blow through it. Those shouldn't even have the dust potential.