These are two values, or rather measures, that indicate the presence of salts and solids in the water in different ways.
The fixed residue or TDS (total dissolved solids) is the degree of mineralisation of water, i.e. the amount of perfectly dry solid matter that remains after the evaporation of a known quantity of water. The fixed residue is like the DNA of water, it contains its essence. Measured in mg/L, it precisely represents the amount of minerals that remain after the evaporation of a litre of water at 180°C. We distinguish:
minimally mineralised water: < 50 mg/l
low-mineral waters: < 50 to 500 mg/l
mineralised water: from 500 to 1,500 mg/l

Electrical conductivity or EC is a parameter that indicates the content of dissolved salts in water. It is called electrical conductivity because the salts are found as charged ions that allow electrical current to flow through the water. If the conductivity value of water is high, the water is rich in salts; if it is low, the water is poor in salts. Water usually has a conductivity of between 100 and 1,000 microsiemens/cm. By law, conductivity must not exceed 2,500 microsiemens/cm at 20°C.

Water with an EC value between 20 and 130 microsiemens/cm is a water with an excellent purifying effect, ideal for the functions of the human organism.