Treated water, limiting hardness and TDS to less than 400 PPM is required to avoid scale formation in the heat exchangers. The scale formation and fouling of this equipment can deteriorate their thermal efficiency and may result in unsatisfactory temperatures in conditioned spaces. As explained earlier, scaling promotes bacterial growth. Besides, scaling increases maintenance frequency and increases maintenance costs. Hence, to realise the full benefits of HMX-Ambiator, it is necessary to use treated water, in case untreated water has high TDS or hardness.