Does it have to be distilled water or is tap water okay for usage?

We suggest using distilled water because tap water will leave hard water deposits on the heating element. Eventually covering it enough to prevent it from heating up. If you choose to use tap water, you can clean the heating element by filling the tank with a 50/50 mix of water/white vinegar, no heat, let it sit for 30 minutes, then o=pour it out. If it comes out milky, that's the hard water deposit. It's easier to use distilled water.