Regarding water, I find the
Rixel Kaul Bottle Klick to be a useful device. Allows you to add an extra bottle mount anywhere on the bike, but also to be able to remove it when not in use. I use it on my Brompton so I can mount a bottle and still fold the bike up. Talking of my Brompton. It wouldn't be a BCUK bike touring thread without me chimbing in my 2 pence worth.
I use my Brompton, Luna, for all sorts of crazy bike tours. And even did the Isle of Man TT course on it in 2016 (66.7kph down hill on a Brompton is pretty terrifying, you can do a 90° corner on it at 40kph, but it does require changing underwear afterwards...)
Brompton make a T bag, which is about 25-30L, and fits on the front of the bike. Which is plenty big enough for many trips. I've added a 30L Alpkit dry bag on the underside of the saddle. This gives you 60L of luggage capacity. Which is more than enough for pretty much anything you'd do on a Brompton...
Luna in Luxembourg:
The T bag does however present quite a large drag coefficient, you certainly notice it. Also by having the volume, I was filling it. So as the front bag basically contained just my food, I replaced it with a 13l alpkit bag. This is enough for 2-3 days food, plus a 1l pot, with a stove inside. I strap this to the handle bars with a pair of webbing straps. Not as fast to remove as the T bag, but much less drag, and encourages me to pack more efficiently.
Luna on a Dutch adventure with the smaller front bag:
Luna approximately 60km into an 80km 2nd day of a 130km trip through the Ardenne. In which I reached the top of both Belgium (694masl) and The Netherlands (322 masl). The front wheel is in Germany, the rear wheel in Belgium, and the bottom bracket is in the Netherlands.
In january I took Luna out for some sub zero lunacy in the Netherlands, it was -6°C, lots of ice, and the offroading down frozen trails was a lot of fun. As I had extra warm weather gear I did that ride with the T-bag and saddle bag config as in the first photo. So as to stay up right on the ice I had studded tyres fitted:
The Brompton isn't exactly the most efficient bike out there, you lose a fair bit of energy in the suspension system, but it does allow for trips you might not other wise do where you can combine public transport with cycling.
My next bike will likely be a cycle cross bike such as the Genesis Vagabond, which I'll also deck out for touring, for those places even I'm not insane enough to try on the Brompton...
J