'water-adding' originates from English, specifically as a compound of the noun 'water' and the present participle 'adding' (from the verb 'add'). 'water' goes back to Old English 'wæter' meaning 'water', and 'add' ultimately derives from Latin 'addere' via Old French and Middle English.

'water' changed from the Old English word 'wæter' into modern English 'water'; 'add' comes from Latin 'addere' which passed into Old French (e.g. 'ajouter') and Middle English ('adden'/'adden'), and in modern English these elements combine productively to form compounds like 'water-adding'.

Initially, the components meant 'water' and 'to join/put to'; combined in modern English they specifically denote 'the act or process of adding water' or something 'that adds water'.