Reference for Eruvin 176:15
אמר ליה אביי והרי שופכין דאדם רוצה שיבלעו וקתני לא ישפוך
R'ELIEZER B. JACOB RULED: IF FOUR CUBITS OF A DRAIN WERE COVERED OVER'Our Mishnah<span class="x" onmousemove="('comment',' Which attributes to the Sages the view that water MAY BE POURED UPON THE ROOF.');"><sup>37</sup></span> cannot represent the opinion of Hananya,<span class="x" onmousemove="('comment',' Since he permitted this only in a courtyard but not on a roof The roofs spoken of were flat and had drains in the form of gutters into which rain water flowed and water was poured.');"><sup>38</sup></span> for it was taught: Hananya ruled: Even if [the area of] a roof was a hundred cubits no water may be poured upon it since a roof is not made to absorb water but to cause it to run down.