I had a recent bad experience with electrolyte drinks tablets. I use them to flavour water with out all the baddies of those tasty but sugary sports drinks or bottled fruit juices, and with a little more variety than plain water. It was a case of not putting the 2 and the other 2 together and coming up with the right answer.
After a long period of using them I noticed that they were affecting my mood, and that I was looking for them through the day if I wasn't able to have regular drinks for some reason feeling my attention flagging. Then the penny dropped, I looked again at the ingredients list and pondered over the mysterious bag of tricks that was listed as 'green tea extract'. Fabulous stuff for weight loss I gathered... and so is caffeine I mused. I checked the manufacturers website, looking long and hard for mentions of caffeine (or caffeine quantities moreover) and found no mention whatsoever.
Now you could at this point be thinking me naive, and I suppose yes I was crediting the makers with perhaps too much in thinking that they would use an extract derivative that was caffeine-free believing that otherwise they would think to state it was a caffeine drink. Long story a little shorter, I eventually looked up a few manufacturers and only found one that made it abundantly clear up front which of their tablets were caffeine containing and which weren't... which leaves me drinking Nuun electrolyte drink. No bad thing given they have more flavours than the first company I tried and are equally widely stocked.
All I can say as any kind of summary is "thank you Nuun!", as someone who finds caffeine throws their sleep patterns, and to a mild but measurable extent affects their mood it is good to find a company that simply puts relevant information there for all to see.
I never did get anything back from one company I emailed with the simple question "can you tell me if there is caffeine in your product?", customer service is a whole other realm of gripes.