With the housing finance market gradually picking up momentum this year, and low interest rates said to be prompting investors to move their funds out of savings products, an emerging issue for lenders is whether they will have sufficient growth in deposits to continue increasing their stable funding ratios and meet growing demand for loans.Based on Australian Prudential Regulation Authority banking statistics released on Friday, this issue has not materialised. Banks' deposit portfolios grew at twice the rate of their mortgage portfolios over the past 12 months and continue to do so.According to the APRA figures, the total book value of banks' household deposits increased by 7.9 per cent in the 12 months to September. Over the same period, mortgage portfolios grew by 4.8 per cent.In September, household deposits increased by one per cent, while mortgage portfolios grew by 0.4 per cent.Macquarie Bank has had the strongest growth among mortgage lenders, increasing the size of its book by 23 per cent over the 12 months to September. Suncorp is up 7.9 per cent over the same period, National Australia Bank and ANZ are up seven per cent, Commonwealth Bank is up 5.5 per cent and ME Bank is up five per cent.Among the big banks, Westpac remains below system, with growth of 1.8 per cent over the 12 months.ING Direct and Arab Bank suffered outflows.In the household deposit market, ME Bank increased the size of its portfolio by 67.4 per cent over the 12 months to September. Other authorised deposit-taking institutions to report strong growth included Investec Bank Australia, which was up 14.8 per cent, HSBC (up 12.5 per cent), AMP (up 11 per cent), Westpac (up 10.2 per cent) and ANZ (up 9.9 per cent).