We recommend using fresh, room temperature water for best results when filling your bottle warmer. Base the water level and setting on the amount of milk in the bottle, not the bottle's capacity.
In most cases, filling your bottle warmer with water to the same level as the milk in the bottle is sufficient (image 2).
For the 2-in-1 Warmer & Sterilizer, you can use the window on the front to check (image 1).
When warming a large amount of milk where the height of the milk in the bottle is above the rim of the warmer, fill the base up to 1 cm/0.4 in below the rim (image 3).