water something down
phrasal verb with water verb uk/ˈwɔː.tər/ us/ˈwɑː.t̬ɚ/
(DRINK)
在（酒精饮料）中掺水，稀释
to add water to a drink, usually an alcoholic drink, in order to make it less strong
(IDEA)
使（观点等）弱化；使缓和
to deliberately make an idea or opinion less extreme, usually so that other people will accept it
The party has watered down its ideals in order to appeal to the centre ground. 为了吸引中间力量，该党已经淡化了其理想。