PS

*biˀr-, *buˀr(-at)- - well, source of water (Fronzaroli 1971: 611, 632, 640; Kogan 2011: 192)

One can easily surmise that the u-forms have secondarily emerged under the influence of b, at least some of them are quite ancient and may reflect a secondary lexicalization of the two variants as early as in PS (perhaps with semantic specification “well” vs. “pit”). Note that for Fronzaroli 1971, 611 *buˀr- is diachronically primary with respect to a more innovative *biˀr-, which is hard to explain in phonological terms.

Akkadian
būru - well; hole, pit (CAD B 335, 342, AHw. 141)
Var. būrtu.
Ebla
BU-rúm - well (VE 520; Conti 1990: 146)
corresponds to Sum. ŠU.A
Ugaritic
biˀr - well (DUL 201)
Phoenician
bˀr - well (DNWSI 141)
Hebrew
bəˀēr - well (HALOT 106)
Hebrew
bōr - cistern, pit, grave (HALOT 116)
probably does not denote ‘well’
Old Aramaic
byr - well (DNWSI 155)
Official Aramaic
byr - well (DNWSI 155)
Nabataean
bˀr - well (DNWSI 141)
Christian Palestinian Aramaic
byr - well (DCPA 47)
Jewish Babylonian Aramaic
bērā - well (DJBA 205)
Syriac
bērā - well (LSyr. 56, SL 114)
Mandaic
bira - well (MD 62)
Arabic
biˀr- - well (Lane 145)
Arabic
burat- - (cooking) pit (Lane 145)
Arabic
b1ˀrat- - a hole dug in the ground in which to cook; a place in which fire is lighted (Lane 145)
Sabaic
bˀr - well (SD 25)
Sabaic
brt - grave (SD 33)
Minaean
bˀr - well (LM 19)
Qatabanian
bˀr - well (LIQ 22)
Geez
barbir - cistern, well, pit (CDG 102, LLA 503)
Harari
buˀur, būr - deep (EDH 39)
Zway
bur - pit, well (EDG 150)
Muher
bʷər - well; hole, pit (EDG 150)
Gogot
bur - well; hole, pit (EDG 150)
Mehri
bayr - well (ML 40)