汚 - Stagnant Water Is FILTHY

Readings & Meanings:

オ

けが（す）

よご（す）

きたな（い）

to soil, to get dirty

Common Usage:

大気汚染

汚職

汚物

汚す (けがす)

汚す（よごす）

Examples:

大気汚染は深刻な公害問題だ。

その市長は汚職が原因で辞任した。

トイレが詰まって汚物が逆流した。汚い！

私の名前を汚す奴は許さない！

Ｔシャツをケチャップで汚してしまった。

Translations:

Air pollution is a serious environmental problem.

That mayor resigned due to corruption charges.

The toilet was stopped up and began to overflow with excrement. It's so dirty!

I will not forgive the bastards who disgrace my name!

Oh man, I got a ketchup stain on my T-shirt.

Radical:

San-zui again, the 水 radical on the left.

The right part is 于, originally a pictograph of a rising object that hits something and then bends.

So 汚 is a pool of water that bends. It doesn't go anywhere, like a puddle, or a pond cut off from the sea.

Water that does not flow becomes stagnant, filthy, and stinky.

Important:

If you're in a restroom in Japan, and you're a lady, you should probably be prepared to see this sign in Japan:

トイレットペイパー以外の汚物やオムツはトイレに流さないで下さい。

汚物 here does not refer to excrement, of course, but rather pads, sanitary napkins, etc.

References:

http://www.kanjinetworks.com/indices/radindex.html
http://www.thejapanesepage.com/node/kanji/e.htm