In South America, they don't usually use the typical American hot water heater that keeps a big tank of water hot and ready-to-go at all times. In fact, when checking into a hotel, it's wise to ask whether they have hot water at all and whether it's available all the time. Sometimes it's only available in the evening. When there is hot water, if it's not heated by the sun, it's usually provided by some type of on-demand device that heats the water immediately before spraying it on you. It's probably more energy efficient, but one disadvantage of this method is that hot water and high pressure are incompatible. The faster the water flowes through the heater, the less it gets heated. You control the temperature by changing the pressure, so if you want a really hot shower, it has to be a trickle.
Sometimes this system is a box with a gas burner in it located somewhere near the shower. You can hear the flames kick on when you turn the water on. But other times it's an electrical device that's integrated into the shower head. Here's the one in my otherwise very ritzy $7 hotel room in Copacabana:
I hate these things. They rarely work as they should, and this one was no exception. Here's what it looked like by the time I actually was able to take a hot shower:
Looks dangerous, doesn't it. Fortunately, I didn't get electrocuted...this time. As often as not, when I use one of these contraptions, it's messed up somehow, and I do. And since they're used where the voltage is 240v, it's even less fun than being electrocuted in America. In Brazil I encountered one with the plastic caps covering the switches missing. The switches themselves were metal, and when I tried to switch it from luke-warm to hot...zap! Another one in Brazil was made entirely of metal, and when I lifted my arm over my head, I inadvertantly touched it and...zap! In La Paz I went into a shower and turned the metal faucet handle on the wall and got zapped. Instead of fixing the faulty grounding, they'd taped the handles, which only lessened the shock.
Fortunately, in my apartment building, there seems to be a real water heater. It must be far away from my bathroom, because it takes a couple minutes for the warm water to arrive, and at least five for all the pipes to warm up and the water to get really hot. But that's a small price to pay not to be electrocuted everyday.