WD518 has 2 additional functions, but lack the freely 180° moveable water outlet and a water tray, everything else exactly the same

1) 10ml volume control - Can set any volume u like every 10ml between 120~1000ml (i.e. 120, 130, 140 etc. all the way to 1000ml)

2) Favourite preset - Can set 3 favourite presets of volume + temperature combo, 1 button to change both volume and temperature you use most frequently
(Preset A = 120ml 40°C for baby formula, Preset B = 270ml 85°C for coffee, Preset C = 800ml cold water for gym bottle etc.)

3) Both has auto up-down water tap (to avoid water spill out, safer hot water use)
But WD518 is square shaped, so once installed, water tap cannot swing horizontally freely (Can still be installed either vertically or horizontally if preferred)

4) WD518 has no water tray - Shorter length by 15cm yet does not affect usage as long as water doesn't overflow

5) Both models same price (whether outright purchase, rent-to-own and the subsequent filter package), unless got promo