BMC excess water billing

Since past 48 years I have been getting bill of rs. 300 to rs. 400, now suddenly have started receiving bills of rs. 00/- To rs. 0/-. In the past we were 8 people in same house now we are only 3, so how does the consumption increase?????? period consumption amount paid not paid may-june 2012 400 6.00 not paid jul-aug 2011 405 9.00 not paid jan-feb 2011 393 1.00 not paid jan-feb 2011 61 7.00 paid apr-may 2011 62 7.00 paid jul-aug 2011 92 4.00 paid oct-nov 2011 389 7.00 not paid jan-feb 2010 61 2.00 paid apr-may 2010 61 2.00 paid jul-aug 2010 64 8.00 paid oct-nov 2010 64 8.00 paid jan-feb 2009 65 5.00 paid