淘's semantic compound is 氵 (“water”). But how does "water" relate to "naughty; mischievous"?
淘 has the meaning of wash
'washing' is related to water
The action of washing is rapid and energetic
淘氣 (mischievous) is mostly used to describe an unruly child and we identify a child as unruly when that child doesn't seem to be able to sit still for a second
淘 itself doesn't contain the meaning of naughty; mischievous