Piping has existed since long before The Union, a human invention like most practical things. However, hot water is a bit more nuance. It’s been around since Peter’s reign, centuries ago. It appeared in the form of a potion.
People say it was one of the first ever alchemy recipes, and they’re half right. See, it was one of the first written alchemy recipes and one of the few that continues to be used to this day. It was discovered at the very beginning of the so-called alchemy revolution in which there was an influx of scholars interested in these studies and many new recipes arose from it.
The potion is called Califeru, though many refer to it merely as the heating potion. They are most commonly made by brewing jasmine tea over an entire week period before adding live philodendron selloum, leaving it for another week and then it is left in the sun for another week.
If this sounds like a lot of work for a hot bath? Well, it is, but fortunately from the moment of invention, there was a business opportunity. Alchemists would get apprentices used to measuring ingredients and controlling temperature by having them make large batches of the stuff. They would then bottle them up and sell them at the markets.
The average potion size was enough for a week’s baths for one person. It was just another thing to add to the grocery list each week.
There hadn’t been much innovation as the potions work pretty perfectly. There have been other methods tested, such as metal water tanks kept on the roof in the sunlight or baths built over candles, but both were far more fiddly and less reliable.
One innovation thought, reserved for large buildings with many rooms, happened in piping. A genius idea to have no one water tank but two. One for the water and another holding the potion, it took some time to get the quantities right but once that was sorted you could open a tap and have hot water directly at your fingertips.
This also allowed for the appearance of showers.
Something fun to know is that when Henry was rebuilding the cottage after Itazu burnt it down by accident, he considered putting in the two tanks despite it’s high cost in exchange for the convenience of showers. But Itazu insisted she could heat up an entire water tank without help.
So Henry had a normal metal water tank installed which Itazu would place her palms on and heat up with her magic. The first few times Henry found he had to pour a bath and wait for the water to cool down, but eventually Itazu figured out the ideal heat. Henry still had a small basket of heating potions though, in case Itazu is not at home for some reason.