Welcome, Rod!

First, take it out of the water, quick! If there is no mushy brown or black forming on the cut surface, pat it dry, and let it dry and form callus for the next 3-5 days. If the cut end is getting mushy, recut it about an inch higher, and then let it dry as above. Once it has dried, plant it about 1/2 in. deep in a mixture of equal parts perlite and sand. staking it to hold it upright, if necessary, and give it bright, indirect light, or filtered sun. Rootone isn't necessary, but sometimes helps it to root faster. Moisten the rooting mixture just before planting, and water again afevery 2 weeks or so. After 4-6 weeks, the tip should start to show new growth with leaves, which tells you that it has taken root. That's when you gently transfer it to a pot of cactus mix--if available--or mix the rooting mixture with regular potting soil, about 1:3 proportions, as a substitute. Don't plant it any deeper than it was while rooting, and keep staking it, if needed. After six months to a year, you can probably take the stake away.

Hope this helps!

gosh yes take it out of the water asap.
The advice given is what I would say. I assume Rootone is a hormone rooting powder. Shouldnt need it really.