Yosef Karo, Translation:Shulchan Aruch — Orach Chaim 537…
“ Paragraph 2 - Even a house of channels is only allowed to be watered when there is not excessive labor involved, like when there is a spring, whether newly-emerged or old, that one can just extend and water the field. However, one should not draw water and irrigate from a pool or from gathered rainwater, because it involves much labor. Even if there is one garden bed, half high and half low, we do not draw water from the low one to water the high one. ”
