It is possible in rare ...

It is possible in rare circumstances to have a hardness that is higher than TDS, due to the difference in the reporting units. Hardness is traditionally reported in "mg/L as CaCO3", while TDS is often reporting in mg/L. The measurement methods are also different, with hardness usually being determined by titration or ICP-AES, and TDS often being determined by dry residue. 

For example, a water sample that contains only 1 mmol/L of MgF2 (magnesium fluoride) would have a TDS of 62 mg/L, but a hardness of 100 mg/L as CaCO3.