Can you start a Christmas cactus by putting the hair piece in water?

https://www.gardeningknowhow.com/ornamental/cacti-succulents/christmas-cactus/how-to-propagate-and-plant-christmas-cactus.htm

No, rooting any succulent should not be done in water. The good news is rooting succulents is simple. Once you've taken your cutting, place the segment in a moist peat and sand soil mix. Insert the segment about a quarter of its length below the soil surface. Place the pot in a well-lit area, avoiding direct sunlight. Do not let the soil completely dry out and at the same time you don’t want it soaking wet so make sure your pot is well drained. It will seem like the water just pours right through.

Good luck with your new cactus!

: )

I've rooted my Christmas cactus in water several times now without any problems. I just did one for my daughter. I guess you can try both ways.

And don't give up if you don't see new growth on the piece you've planted in the growing medium. It can take up to 6+ weeks

No need to start your Christmas Cactus in water.......just take a 4-6 inch start off from a plant and put directly in potting soil....I usually put at least 5-6 starts in a pot, water well, place in a sunny window and water weekly! Good luck!