A lot of these suggestions are cool, literally. But for touring they are kinda posh. Where are we getting clean ice out there in the waterless wilderness. If you come up with a way to carry water that only works on your local runs, it will be of limited usefulness, though it may bridge you to a greater fitness level.

Tubus racks are awesome, and you'll be very happy with them. In terms of carrying water, you have a few options.

Mount bottle cages everywhere you can. Depending on the frame size, most touring bikes can handle three or two (for short folks like me). That's enough water for an hour or two, but what then?

• You can pack some water bottles into a pannier or a rack pack. Harder to get to, but when you're touring you've already got the bags on. Front panniers are great for this, since you can get to them while straddling the bike.
• If you have the room on your seatpost, you can get a double bottle cage that mounts behind your saddle.
• Ortlieb panners will accept water bottle cages, but you have to do a little surgery on your panniers, and you can't use standard cages. Handy if you already have those bags, but they can be finicky.
• I keep a camping roll strapped to the top of my rear rack, and can usually find a place to bungee in some water bottles. If you're clever, you can get to these without getting off the bike.
• Camelbaks are great if you don't want racks or bags. I use a water bladder when backpacking, but never on a bike. Why get my back all sweaty when I have a bike to carry stuff for me?

In the Midwest was able to ride a century with two 8 oz water bottles many times.

A framepack with a water bladder would make it easy to carry an additional 3 liters.

I generally find that for me two bottles is plenty for 32 miles even in the heat and I can generally go twice that far on that much water, but where I have needed extra water and there was no pannier space a couple bottles or 1 liter bladders in my jersey pockets worked well enough. If I have panniers on and have space in them I use them, but in a pinch the jersey pockets work.

I even managed that once in Texas for a stretch of 90 miles or so during a tour of the Southern Tier where I was away from chances to refill for over 24 hours, so I had to have enough to drink all day, cook dinner, sponge off, and ride to my next resupply point in the morning. My jersey pockets were jammed full of water bottles to the point of sagging badly though

Another option might be to use a camelbak. Fill it with ice and the cool on your back can be quite pleasant on a hot day. I don't usually use one, but I did do one tour with one and it worked fine.