Akademik

как воздух
КАК ВОЗДУХ нужен, необходим и т.п. кому
[как + NP; Invar; adv (intensif)]
=====
(s.o. needs some person or thing) very much:
- X нужен Y-y - - Y needs X as much as the air Y breathes;
- X is as necessary to Y as the air Y breathes;
- Y needs X as much as air to breathe.
     ♦ После падения Франции я не раз встречал людей... разлагаемых потребностью политической деятельности... Им надобна как воздух сцена и зрители... (Герцен 1). After the fall of France I more than once met people... who were disintegrated by the craving for public activity. ...A stage and spectators are as necessary to them as the air they breathe... (1a).
     ♦ Главное было передохнуть... Передышка нам была нужна как воздух (Мандельштам 2). ...The main thing for us was to have a break. ... We needed this as much as air to breathe (2a).

Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. . 2004.