The natural range of deuterium in drinking water on Earth is 90 to 160 ppm. Where you fall within that range depends entirely on where you live — and almost nobody tracking their health knows this. The measurement data comes from István Fórizs — Hungarian geochemist and isotope hydrologist who studies the movement and distribution of isotopes through water systems in nature. Ocean water carries 156 ppm — the reference point and the highest deuterium concentration found in liquid water under normal conditions. Tropical and high-evaporation lakes such as Lake Chad and Lake Van in Turkey sit at approximately 160 ppm because evaporation concentrates deuterium — lighter water evaporates first and heavier water remains. Mediterranean precipitation trends toward the higher end of the range. Northern Europe trends progressively lower moving north. Greenland and Antarctic ice sit between 90 and 110 ppm — the most deuterium-depleted natural water found on Earth's surface. The continental effect explains the geography. Water evaporating from the ocean forms clouds. As those clouds move inland, each rainfall removes heavier isotopes preferentially — the remaining vapor becomes progressively lighter. By the time precipitation reaches the center of a continent it carries significantly less deuterium than coastal rain. Temperature adds another layer. Precipitation in Budapest measures 152 ppm in summer and 132 ppm in winter. A 20 ppm variation driven purely by temperature — the same city, every year. But tap water tells a more complex story. Most drinking water in Hungary comes from groundwater — an accumulated average of precipitation over time that leans slightly toward winter values because winter precipitation infiltrates the ground at higher rates than summer precipitation, which tends to evaporate before reaching the aquifer. Some of that groundwater infiltrated the earth during the ice age — over 11,000 years ago — when global temperatures were significantly lower. It carries less deuterium than modern precipitation from the same region because the planet was colder when it fell. The geological record of temperature is readable in the deuterium content of ancient groundwater. Which means the deuterium content of your drinking water is shaped not just by where you live today — but by the climatic history of the region over thousands of years. The gap between ~90 ppm Antarctic melted snow and ~160 ppm tropical/evaporative water spans most of the biologically active window that Professor Roman Zubarev from Karolinska Institute identified as regulating cell growth. Your mitochondria are navigating this variable every single day. Geography is a biological input.