朱熹
半亩方塘一鉴开，
天光云影共徘徊。
问渠哪得清如许，
为有源头活水来。
Zhu Xi
A square pond, half a mu, like a mirror,
Sky-light and cloud-shade coupled to wander.
What makes the pond so limpid, you wonder?
Because it is sourced by flowing water.