Westpac's much maligned multi-branding strategy appears to be driving a surge in retail deposit growth within the group, according to the latest APRA banking data.Australia's oldest bank outpaced its major banking rivals in household deposits in the year to the end of August after growing by 7.6 per cent.Westpac now holds retail deposits of more than A$200 billion compared to $186.2 billion in August 2016.The trend is likely to present a few headaches for Commonwealth Bank, which has aggressively lowered deposit rates in the last 18 months to preserve margins.CBA was the slowest-growing major bank among depositors during the 12 month period, managing to expand its retail base by only 4.1 per cent to $245.3 billion.While Westpac's flagship rates on bonus saver accounts and term deposits are mostly more generous than those offered by CBA, its outperformance was partly due to its specialist home lending arm, RAMS.The subsidiary is now a price leader in the bonus saver market, through its online saver account that offers depositors a total annual return of 3 per cent.The account is marketed as a genuine savings product, with the monthly bonus interest of 1.65 per cent foregone if customers make a withdrawal.CBA's bonus saver accounts - the flagship-branded Goal Saver and Bankwest's Hero Saver - offer depositors a return of only one basis point if they make a withdrawal during a calendar month.ANZ was an inconspicuous achiever in the 12-month period after expanding its deposit book by 7 per cent or $7.58 billion to $115.4 billion.NAB's award-winning bonus saver account marketed through its UBank arm helped to generate solid year-on-year growth, but could not match the market gains realised by ANZ and Westpac.According to APRA, NAB expanded its retail base by $6.21 billion or 5.3 per cent to $115.2 billion.ING Direct remains the fastest growing deposit-taker among the leading market players, with its consistently aggressive pricing strategy pushing its deposit base up 15 per cent to $28 billion.