use Group by
in your statement :
select mn.meter_name, m.meter_number, m.meter_location, r.rates_meter_rate, r.rates_meter_PPD, m.meter_ID, mt.metertracking_periodend, mt.metertracking_read, mt.metertracking_readend FROM db_meters m, db_meters_name mn, db_rates_meter r, db_meters_tracking mt WHERE m.ICP_ID = '227' AND m.meter_name_ID = mn.meter_name_ID AND r.meter_ID = m.meter_ID AND (r.rates_meter_start <= '2013-08-31' AND r.rates_meter_end >= '2013-08-31') AND mt.meter_ID = m.meter_ID group by meter_ID ORDER BY ABS( DATEDIFF( metertracking_periodend, NOW() ) )