Hello, the answer to whether to preboil your water is the dreaded "It depends."
If you use a sterilizing method that keeps the water/steam at boiling for 10 minutes or longer, the answer is "No" to preboiling - the water is sterilized along with your devices.
If you use a baby bottle sterilizer, microwave sterilizer or similar, the answer is "Yes" to preboiling - the water is not kept at temperature for 10 minutes or longer.

I have chosen an old-fashioned method - once a week, I place a round silicon mat (pot holder) in the bottom of my 3 quart saucepan, place the items to sterilize & cover with water. Bring to a boil, set my timer to 11 minutes and do chores nearby. When the timer rings, I turn off the heat, cover the pot and let everything cool. There it is - one chore & done. No need to boil and bottle (in sterile containers, which must be sterilized each time) water, have another device on hand, etc.
Notes: This method works everywhere - home, winter home, camper, friends' homes...without carrying extra stuff from place to place.
The (optional) silicon mat keeps things from being in direct contact with the bottom of the pot - I accidentally melted the mouthpiece of my Aerobika once on a "hot spot" on my propane range.
A small crockpot, turned on high, also works - I run it for 2 hours and turn it off.
Sue