When copying from 𝓞 to 𝓟, Oliver Cowdery interpreted the original manuscript’s deph (in the hand of scribe 3) as the plural depths, although one could also interpret deph as representing the singular depth. Thus the question is whether deph stands for depth or depths.
Possible evidence that deph stands for depths can be found in Nephi’s version of Lehi’s dream, where the plural is used to refer to this same fountain of water:
Generally speaking, we have the plural depths in the Book of Mormon text: “depths of the sea” (14 times), “depths of the earth” (4 times), “depths of sorrow” (1 Nephi 16:25), and “depths of the mysteries of him” (Jacob 4:8). When actually measuring physical depth, the singular is of course used (“the depth of the ditch” in Alma 49:18).
The only other place in the text where we get singular/plural variation for depth(s) is in the phrase “depth(s) of humility”. In the current text there are five occurrences in the plural but one in the singular (Alma 62:41). Yet even for this one case, the original manuscript initially read depths. But in correcting the following word, Oliver Cowdery accidentally erased the final s of depths, thus leading to an incorrect “depth of humility”. For more discussion, see Alma 62:41.
Thus the text is consistent. Unless the actual measurement of depth is meant, the plural depths is used. Given this consistency, plus the clearly corrupt spelling deph in 𝓞 for 1 Nephi 8:32, Oliver Cowdery’s emendation to depths is most probably correct.
Summary: Continue to follow Oliver Cowdery’s interpretation of the scribal slip deph in 𝓞 as the plural depths.