Get thee a pint mug and some fruit squash. Defeat the bugs by dilution, knowledge and MATHS.
Bugs multiply exponentially, doubling every 20 minutes.
Drink pint of squash. Refill glass.
Drink contents when you've been for a pee.
Repeat six times, them stop.
A technique I've used to good effect in the past, and it appears to be working now. Typically, I first noticed symptoms while on the train this morning, which is a fairly bad place for anything requiring frequent toilet trips. I made do with drinking my remaining water supply on the (thankfully recumbent) ride back from Mordor Central, and following up with a bottle of Frijj and a pint of dilute orange when I got home.
Large volumes of fluid like that tend to result in IBS consequences, but I think I've headed those off with pre-emptive Buscopan. And yet another attack of the poo is better than letting these things fester.
Cranberry juice, on the other hand, is ming of the highest order, and makes obtaining Trimethoprim at short notice seem like fun (cystitis, like hearing aid failure, is one of those things that usually happens at the start of bank holiday weekends).