Method for determining the hydration of a human body, or of a segment of the human body, comprising the steps performed by a visualizing and processor device: determining values each of a mass or volume fraction of intracellular water (ICW P) and a mass or volume fraction of extracellular water (ECW P) of the human body or the segment using a measurement unit, wherein the measurement unit performs a bioelectric impedance spectroscopy measurement with regard to the human body; defining a two-dimensional parameter space with a mass or volume fraction of intracellular water (ICW P) and a mass or volume fraction of extracellular water (ECW P) as separate parameters; determining a reference line within the parameter space, which represents associated values for each of a mass or volume fraction of intracellular water (ICW P) and a mass or volume fraction of extracellular water (ECW P) of a number of healthy subjects; locating a position within the parameter space which corresponds to the associated values of the mass or volume fraction of intracellular water (ICW P) and the mass or volume fraction of extracellular water (ECW P) of the human body or the segment; determining a distance between the position and the reference line; deriving a mass or volume, or a mass or volume fraction, of hydration from the determined distance for the human body or the segment; determining a body fat mass by subtracting the mass or volume fraction of intracellular water and associated materials and the mass or volume fraction of extracellular water and associated materials from a total body weight using an equation: BF = 100 − d ECW ⋅ ECW + d ICW ⋅ ICW, wherein d ECW and d ICW are the densities of respective extracellular and intracellular fluids and associated materials, and ECW and ICW are respective volume fractions in units of [%]; deriving a mass or volume fraction of normally hydrated adipose tissue mass (NH_AT) from the body fat mass by dividing the body fat mass with a factor θ accounting for water and associated materials in adipose tissue, wherein θ is selected between 0.70 and 0.90; and determining a mass or volume fraction of a normally hydrated lean tissue mass (NH_LT) by subtracting the mass or volume fraction of a normally hydrated adipose tissue mass (NH_AT), and the hydration index from the total body weight: NH _ LT = 100 − BF / θ − HYD in units of %; visualizing the results of the measurement and the processing to the user using a user interface. determining values each of a mass or volume fraction of intracellular water (ICW P) and a mass or volume fraction of extracellular water (ECW P) of the human body or the segment using a measurement unit, wherein the measurement unit performs a bioelectric impedance spectroscopy measurement with regard to the human body; defining a two-dimensional parameter space with a mass or volume fraction of intracellular water (ICW P) and a mass or volume fraction of extracellular water (ECW P) as separate parameters; determining a reference line within the parameter space, which represents associated values for each of a mass or volume fraction of intracellular water (ICW P) and a mass or volume fraction of extracellular water (ECW P) of a number of healthy subjects; locating a position within the parameter space which corresponds to the associated values of the mass or volume fraction of intracellular water (ICW P) and the mass or volume fraction of extracellular water (ECW P) of the human body or the segment; determining a distance between the position and the reference line; deriving a mass or volume, or a mass or volume fraction, of hydration from the determined distance for the human body or the segment; determining a body fat mass by subtracting the mass or volume fraction of intracellular water and associated materials and the mass or volume fraction of extracellular water and associated materials from a total body weight using an equation: BF = 100 − d ECW ⋅ ECW + d ICW ⋅ ICW, wherein d ECW and d ICW are the densities of respective extracellular and intracellular fluids and associated materials, and ECW and ICW are respective volume fractions in units of [%]; deriving a mass or volume fraction of normally hydrated adipose tissue mass (NH_AT) from the body fat mass by dividing the body fat mass with a factor θ accounting for water and associated materials in adipose tissue, wherein θ is selected between 0.70 and 0.90; and determining a mass or volume fraction of a normally hydrated lean tissue mass (NH_LT) by subtracting the mass or volume fraction of a normally hydrated adipose tissue mass (NH_AT), and the hydration index from the total body weight: NH _ LT = 100 − BF / θ − HYD in units of %; visualizing the results of the measurement and the processing to the user using a user interface.