Lots of options here. If you ride in areas with businesses, you can buy water or ask restaurants to fill your bottles -- I've never had one refuse. If you ride in rural areas with people but not businesses, you can fill your water from a church spigot (always works) or stop by a house and ask if you can fill from the spigot. The vast majority will fill from the tap. I think I've only had one person ever not let me have any water at all in the past 30 years. If you are in areas where there are not even homes, you can plant water in strategic locations by the side of the road.

Don't forget electrolytes if you're sweating that much. It can be a big deal.

BTW, losing 7.8 lbs in two hours is insane. 4 lbs/hr with temps in the 80's sounds high -- that's two quarts per hour. More of a hot desert type of rate loss. Hopefully, there was an issue with your scale or some other factor was at play but it's likely you were dehydrated. Don't get that far behind on water -- seriously. You go from riding along thinking you're fine to passing out so fast you won't even realize what's going on. You will have more fun and put out better power if you take care of yourself.