'water-filled' originates from Modern English, formed by combining the noun 'water' and the past participle 'filled' (the participial form of 'fill').

'water' comes from Old English 'wæter', from Proto-Germanic '*watōr'; 'fill' comes from Old English 'fyllan' (to fill). The compound 'water-filled' is a straightforward Modern English formation using these elements.

Initially it meant 'filled with water' and this basic literal meaning has remained essentially the same in modern usage.