Hello Meurig,
My own thoughts are that if you were unfortunate enough to be captured in this war, it was still rather better than being captured in the future wars of the next century.
To be honest I think life actually on campaign in South Africa for your average Mr Atkins could be pretty damn rough without being captured.
However, life at that wretched "school" in Pretoria or at Waterval cannot have been much fun, fortunately it only lasted for a few months, but, the conditions, or indeed, lack of reasonable conditions, were indeed, dire, as you say, I would think the lack of ablutions, in particular, a real breeding ground for disease to run rife, combined with a total lack of proper medical facilities.
It does make you wonder just what the military objective of the enemy was, to invade the colonies and to have made no arrangements whatsoever, one wonders if they had actually considered taking prisoners in the first place.
All told, beyond the appalling conditions, generally speaking, the Imperial prisoners were not subject to the torture, slave labour and on occasion, murder, that men were in the last century, I do, however, believe some of the Colonials had a far harder time, in particular the Rand refugees, but, as a serving soldier, you make your bed and you lie down within it.
Moreover, if you don't, there were always men like Bernhard Moller who would do it for you and I certainly would not have liked to find myself in Gibney's boots.
I hope you find that POW on day.
Regards Frank