Easy but better use a PROFESSIONAL drill to look pro     

Haha jokes aside what you will need is a 500rpm or slower mode in the drill driver.

No need to worry, use spade bit and drill slowly on NON-hammer mode, tile depth u can get from tile edge or so, once u gone past (not just the tip) the dust will change colour (from tile colour/white) to cement mortar colour.

Per hole:
Expect to take 8-10mins best case, or >30mins if hardwearing floor tile used as wall tiles.

Please check + axes of any water points to avoid water spout problems.

Up to 10 holes can lah
https://shopee.com.my/Wately-Battery-Cordle...16468.717597438

If you need a lot of holes (not just water heater)..but mirror, towel rail, etc..
Just buy the latest Bosch GSB185 metal chuck  drills more accurately than plastic chuck
https://shopee.com.my/BOSCH-GSB-185-LI-Cord...682.20309501938
pao with 2AH + charger for RM459

Spade bit 6mm
Buy a few and keep, in case ur tile very hard.
https://shopee.com.my/Navato-Glass-Bits-(6m...0761.6583249403
These are consumable items IMO and contractor don't really want to drill tile because time consuming.

China drill OK lah but won't be a "family heirloom"
The cheap china drill better buy w 2 batteries.

1) may be hard to find batts
2) tile drilling makan battery coz 8-10min best case per hole. U need to go slow (<500 rpm) gear otherwise u just polishing ur drill bit. Its like peeling onion layer by layer due to the tile material.

I just use Bosch GSB 550 Professional Impact Drill with the included masonry drill bit to punch a hole in the wall tiles (ceramic)...no issue with the correct method... make sure to place masking tape on the slippery tiles to help direct the opening

Based on water valves, drains, and inlets on the wall, I'm only guessing where the pipes might be.

I've never used a cordless drill before, but the GSB 120 is capable of drilling masonry and tiles, so it should be good. If you are uncertain about the method, you can look up how to drill on tiles on YouTube. Make sure to use the sharpest masonry drill bit you can find. The masonry drill bit that comes with the Bosch drill can do the job as well.

The Bosch model code indicates the function; the one with a hammer function appropriate for masonry drilling is marked GSB; otherwise, it is simply GSR.

The GSB 120's chuck can only accept drill bits up to 10 millimeters in diameter, and I'm not sure if it will accept a 10mm drill bit for masonry drilling.

UPDATE: