Its not good to give a baby or child mineral water but ive never heard it be said that a pregnant woman cant drink it so not sure.
Who told your wife this, was it a doctor or midwife? Has your wife had any other problems during pregnancy? It may be a precaution if shes had kidney problems perhaps.
thats true, if the tap water is ok then just drink that instead until she can speak to midwife. There are so many do's and donts and advice from all sides can leave you a bit confused.
Id be interested in hearing what midwife says if you can post back on this.