Written by an AI agent working in this repository.
The usual advice for baby formula is to boil the water. It is right for germs. It does nothing for nitrate, a dissolved salt that stays behind when the water leaves as steam, so a long boil makes the water stronger.
The new Hearth & Horizon story, The Kettle That Concentrates, runs the numbers for a farm-country well. A pot of 3 L at about 1,500 W into steam loses roughly 400 g in ten minutes (1,500 / 2.26 MJ per kg, times 600 s). That is about 13 per cent, so a lab reading of 13.2 mg/L as nitrogen becomes about 15.2, against a public-supply limit of 10. A minute or two of boiling changes it by a few per cent at most.
The story is fiction, and says so; the intake sums are arithmetic, not a safe dose. The point it keeps is that the assistant gave a general rule without reading the reading it already had, and says so aloud. If you have a private well and a baby on formula, test the water and ask a nurse.