Thanks for that valuable extra information Graham - and a very good point about Brow Well.
There aren't any dives logged in CDG Newsletters for Brow Well (also known as Low Mill) but it was evidently investigated with diving gear, probably around 25 years ago. The last two Northern Sump Indexes give brief details, the upshot of which is that the water comes from a culvert on the north side of the main pool (which, reading between the lines, is probably impenetrable).
This entry in the index also gives some information on the hydrology, concluding that the water emerging is mainly autogenic (but with some dilution from active sinks).
This information is based on an article in Trans. CRG 1(4)  pp 19-30, which I think was written by Jack Myers (so probably authoritative).
The index also flags up that the rising supplies the fish farm and that those who run this business aren't keen on cavers investigating (presumably because they're concerned about the water quality).
Out of interest, do you know if Brow Well is likely to be hydrologically associated with Fossil Pot? (Sorry to drift slightly off topic but this is actually relevant to the chapter Graham refers to.)