Find below a useful guideline of water quality standards in heat exchangers, compliant to the standard JRA-GL-02-1994.
For all cases, cooling water, cold water and warm water, at mid-low temperature and high temperature, the technical sheet provides the maximum quantity for all main chemical elements that can be contained in the water, also referring to the possibility of corrosion and scaling.
Obviously, also paying attention to other engineering values, such as pressure design, temperature design and thermal gap limits between primary and secondary circuit.