TDS and pH are two different indicators of drinking water that need to be tested.
TDS is called Total Dissolved Solids, which can be approximated as the salt content of the water. The larger the TDS value, the higher the salt content of the water, and the smaller the TDS value, the lower the salt content of the water, and the purer the water. Drinking water TDS value is generally in the 600mg / L or so.
pH indicates the acidity of water, pH>7 is alkaline, pH higher alkaline stronger PH=7 is neutral PH<7 is acidic, pH smaller acidic stronger. Nowadays, drinking water is formulated in various ways, the pH value is not fixed, neutral and slightly alkaline is better.