take to sth like a duck to water从字面上理解，也就是指某事像鸭子入水一样。鸭子入水是很容易的，如果某事如鸭子入水一样，也就是指做某事非常容易，因此便有人将这句习语引申为轻而易举，毫不困难，毫无畏惧（习惯于某事）。

【例句】
She has taken to teaching like a duck to water.
她教起书来轻而易举。

The new playground is very popular. The kids took to it like ducks to water.
新修建的儿童乐园特别热门。孩子们简直是如鱼得水。