Part of the availability of drinking fountains may be affected by climate, particularly where plumbing is vulnerable to freezing damage. If it's like most parks and recreational area budgets, improvements move very slowly.
We're fortunate around the Fort Worth area. There's at least tepid water available in several places along the popular Trinity Trails and adjacent cycling paths. Several private businesses, bars and churches provide water and even repair stations. Most brewpubs I hang out at have a tap for "extra-lite beer (water)" or a cooler full of water. They can move a lot quicker than gummint, and it helps earn the loyalty of cycling customers. We often schedule our casual and social group rides around stops at those businesses that welcome cyclists.
So I can usually get away with toting one bottle on city rides, or the 5 mile training circuit that's only a mile from my home. If I'm doing laps, I can always go back home for a refill after three laps. There's always either a fountain, water dispensers or a convenience store within a mile or two. I drink lukewarm tap water at home so the temperature doesn't bother me. The only time I prefer cold water is after a hard workout, but not necessarily after every ride in summer heat.
I suspect some folks who prefer the flatter, faster routes along the Trinity river don't carry water at all on certain Strava segments because they can stop at the church or Mellow Johnny's for water, the water fountains along the trail, or the Y at the end of the line in Benbrook near the lake.
And it's a reasonably cycle friendly area, with lots of folks riding in rural areas too. It's not unusual now to clomp into pretty much any convenience store, fast food joint or even homestyle food restaurant wearing clipless shoes and Lycra. Interesting changes from the Texas I grew up in.
I do pre-freeze water with electrolytes in my Polar insulated bottle, about half full of frozen slush, the other half topped off with water. I can refill it a couple of times and it'll still be cool during a ride.
For longer rural rides I usually carry two or more bottles. On seriously hot days I'll tote a stainless double insulated thermos that accepts standard water bottle tops. Pre-frozen electrolyte solution will stay frozen for up to 12 hours in summer heat. It's heavy but worth the weight on those 50+ mile summer rides.
I also have a Mylar pouch that holds about a pint. I'll freeze it too and stick it in my middle back jersey pocket. Saved my bacon a time or two on long hot rides when I misjudged the distance to the next convenience store.
So far the only time I've run out of water on a rural ride, I stopped to ask some folks at a disc golf course if there was a water fountain around. They just gave me a bottle of water. Got me to the next convenience store a few miles away. That's when I started carrying that Mylar pouch of frozen electrolyte/water as a backup.
This summer I've noticed some older folks like myself misjudging their hydration, despite years of experience. I suspect they're mostly misjudging the effects of aging. And this July isn't quite as hot as last year. Last July we had several consecutive 100+F days. This July has mostly been mid to high 90s, and pretty humid. It almost feels cool when we're moving due to the cooling effect of humid air and wind. But it can fool us into drinking less than we need. I got a little dehydrated Sunday a week ago on a 55 mile ride, and it suddenly caught up with me right at the 50 mile mark. I realized I hadn't even finished my two 24 oz bottles, although I did drink a big cup of iced coffee during a pit stop. I was pretty wiped out the next day, but was fine by Tuesday. After that I started drinking whether I felt thirsty or not. Worked great, felt fine during and after 50+ mile rides in the heat on Tuesday and Thursday club rides.
I also carry spare packets of DripDrop electrolytes in little single serving Mylar packets. Helped revive one fellow who was on the verge of heat exhaustion a couple of weeks ago, and a woman last week who fainted and vomited clear water. She'd just switched to NUUN which, in my opinion, doesn't have enough sugar to help rapidly absorb water. Hard to convince some folks who are calorie conscious, but most of us re-hydrate better after being overheated when there's a little sugar or honey in our water/electrolytes. Doesn't need to be as sweet as Gatorade or other sports drinks. But that zero calorie stuff or artificial sweeteners just doesn't work as well for many of us. DripDrop is a bit pricey, although no more so than NUUN, and handier to carry. I always tote a few extra packets in my saddle bag, jersey pocket, etc., both for myself and anyone who's suffering heat exhaustion.