15 month old attitude and tantrums. Need advice on how to deal

*sigh* my sweet innocent baby is a 15 month old with the worst attitude. She is my first and only child. I feel like I am raising my voice more often and I just don’t like it but i HAVE to sometimes to get her to listen. When she tantrums husband and myself just lets her tantrum it out. And I calm her afterwards. It’s soooo bad. Examples: if I’m testing the temperature of the water in her bath, putting my hand under the faucet she will smack my hand out of the way and if I put my hand back under the faucet she throws her self to the ground crying. If you take something from her she throws herself on the ground crying. She does this whine thing(not crying) and in a panicky way. When she does this I tell her “everything’s okay, be patient”. I catch myself in a stern voice and loudly say”Harlow” way to often these days. I do that when she is about to start a tantrum sometimes this stops her. Sometimes it doesn’t. She is insanely smart, she knows how to put a usb cable in a usb slot. She knows how to fill cups under the water faucet. The list goes on. I need advice. Please tell me different ways on how to deal with her tantrums. I want her to understand peace, understanding she can’t have everything due to it being dangerous or I just don’t want her to have it. Help. Help.