Bank account

It is  always advisable to disclosed all bank accounts to the Clients

In case of Non disclosure, consequences can be seivour 

IT officer if got suspcious or have any information related to other bank accounts which is not disclosed

he may order you to bring or make addition to the FY relevant to the AY 

and can also bring re-opening of earlier AYs.

Kindly read Section 147 Reassessment where assessment has been made u/s 143(3) or 147

It is always better to disclose all transactions (not only bank interest)and the closing balance in the balance sheet. For a proprietor, all his assets and liabilities, whether business related or not, should appear in BS.

However, if you can prove that all the amounts credited to a particular undisclosed bank account (for eg, rent/ interest etc)are taxed in all the years from start, the AO may not make addition.