What does "swim dirty water" mean?
Listening "I'll Be Waiting", I came across the expression "I swam dirty water". Above all, I need to know if it's a common idiom in spoken English. Secondly, I would thank you if you could explain its meaning to me."I'll Be Waiting" by Adele;
Hold me closer one more time,
Say that you love me in your last goodbye,
Please forgive me for my sins,
Yes, I swam dirty waters,
But you pushed me in,
I've seen your face under every sky,
Over every border and on every line,
You know my heart more than I do,
We were the greatest, me and you,

Question

What does "swim dirty water" mean?
Listening "I'll Be Waiting", I came across the expression "I swam dirty water". Above all, I need to know if it's a common idiom in spoken English. Secondly, I would thank you if you could explain its meaning to me."I'll Be Waiting" by Adele;
Hold me closer one more time,
Say that you love me in your last goodbye,
Please forgive me for my sins,
Yes, I swam dirty waters,
But you pushed me in,
I've seen your face under every sky,
Over every border and on every line,
You know my heart more than I do,
We were the greatest, me and you,

Answer

It is not a common idiom. Even a native speaker has to glean the meaning from the context.

This context suggests that "I swam dirty waters" refers to the same activities referenced in "please forgive me for my sins": swimming in dirty waters means living in dirty, or sinful, situations-- doing dirty (unclean, impure) things. The following line "but you pushed me in," then, means that the person she is addressing pushed her into those situations-- that is, his behavior forced her to act the way she did. 
(A common English idiom for this is "you drove me to do it.")

Hope that helps!