In simple English, hotels use a central boiler system to heat the water for the whole facility. Here's how it works.
Water, from the city system, is connected to a main inlet water valve at the hotel's boiler plant, somewhere on the property. The water the hotel system enters at around 50 degrees (F) and is distributed, via centrifugal pumps that maintain the water pressure, to numerous huge boilers. How many boilers depends on the size of the hotel; some have two boilers, some have six, some even have eight.
The boilers run on natural gas or oil. At these quantities, there's not much price difference between the two. They raise the water temperature to upwards of 150 degrees at a pressure rate of about 25 gallons per minute per boiler. The hot water is transferred by a heat-pump water-loop system, which increases or at least maintains the current water temperature.
Hot water for the guestrooms sits in storage at about 160 degrees, which is then tempered down to 110 degrees before it enters the guestroom DHW (domestic hot water) loop.
Other areas of the property, the kitchens for example, must have a DHW temperature of at least 140 degrees to pass code (dishes must be washed via dishwashers utilizing water heated to no less than 140 to be effective against bacteria).
The "loop" returns the unused hot water back to the boilers at a temperature of about 70 degrees (F), which is optimal for the process to repeat the cycle. This is required, because not all rooms are rented every night and the water would become stagnant or even rusty after a while. The loop allows the hot water to be used on demand. Say you have a floor with 50 rooms and only one room is rented. That room, if occupied by a hot water hog, will be permitted to use all the hot water allocated to all of that floor's rooms. Meanwhile, the loop keeps replenishing the allocation. The return lines send the piped water through a big loop back to the boilers; otherwise it would get cold sitting in the line of a big empty hotel.
Most casinos use either stairwell or service-elevators space to house the insulated pipes to transfer (and sometimes holding) stations located on each floor. From there the water is directed to each separate room via copper water pipes. Upon entering the room, the water is further piped to the different functional outlets, such as the shower, the sink, the toilet, the wet bar, the hot tub, etc.
Some of your finer hotels use the Paloma-style gas heater, which is a separate stand-alone unit, installed inside each room in the facility. It's about the size of a clothes hamper with a moonshiner's still-like copper coiling system that pressurizes the water and forces it through the copper coils while ignited gas heats the copper coils to almost 150 degrees. This all happens as fast as you can turn your shower on. There's no water storage and no creaking pipes.
