The solubility of some minerals, such as lead, increases drastically with higher temperature (https://www.bbc.co.uk/bitesize/guides/z4s48mn/revision/2 https://w

The solubility of some minerals, such as lead, increases drastically with higher temperature (https://www.bbc.co.uk/bitesize/guides/z4s48mn/revision/2 https://www.bbc.co.uk/bitesize/guides/z4s48mn/revision/2). Hot water will have much higher concentrations of those minerals compared to cold water. This is not a closed-system, steady state flow equation, since the hot water can pull in additional chemicals from its environment: metal or plastic pipes, fittings, anode rods (aluminum and zinc). The lining inside the hot water tank is made from many different materials, including synthetic polymers (https://www.bijlibachao.com/water-heaters/coating-storage-water-heater-thermoplastic-stainless-steel-enamel-coating-glasslined.html https://www.bijlibachao.com/water-heaters/coating-storage-wa...), which can degrade over time and leach more chemicals into the hot water. Finally, bacteria (e.g. Legionnaires) can grow in the water tank if the water is not hot enough. This article from the Denver water department says, don't drink the hot water: https://denverwatertap.org/2017/12/13/psa-dont-drink-cook-hot-water-tap/ https://denverwatertap.org/2017/12/13/psa-dont-drink-cook-ho...