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.