If it were not for water, nothing could live. （関西大 <改>）
もし水がなければ，何も生きることはできない。
以下は全て「Aがなければ」を表す表現です。
(1) if it were not for A = were it not for A （仮定法過去）
(2) if it had not been for A = had it not been for A （仮定法過去完了）
(3) but for A
(4) without A
with A は「Aがあれば」を表し，ちょうど逆の表現になります。
(5) without A ⇔ with A
With a little more care, you wouldn't make such a silly mistake. （ロイヤル英文法）
もう少し注意していれば，
Without appropriate software, a computer would be a mere box. （ロイヤル英文法）
適切なソフトがなければ，