Risks to financial stability "are primarily macroeconomic in nature, rather than direct risks to the stability of financial institutions", the Reserve Bank of Australia's declared in its Financial Stability Review, released on Thursday.The April 2017 edition of this half-yearly report shares public domain versions of analysis no doubt considered this year among the Council of Financial Regulators, culminating in APRA's outline of additional macroprudential measures at the end of March.The RBA's FSR surveys orthodox topics but adds colour on the data behind APRA's actions, especially that on interest-only mortgage lending.Aggregate mortgage buffers - balances in offset accounts and redraw facilities - "are high, at around 17 per cent of outstanding loan balances or around 2½ years of scheduled repayments at current interest rates," the RBA writes, an estimate to which it adds a caveat."These aggregate figures mask significant variation across borrowers, with available data suggesting that around one-third of borrowers have either no accrued buffer or a buffer of less than one month's repayments. "Those with minimal buffers tend to have newer mortgages, or to be lower-income or lower-wealth households," the FSR says, in analysis drawing on data from back in 2014.Households staggering into a position of zero wealth will soon leave a mark on bank asset quality, the RBA suggests."Weak economic conditions, and declining housing prices, continue to present challenges to the financial health of households in regions with large exposures to the mining sector." "The rate of personal administrations in Western Australia increased further over the second half of 2016. While commodity prices have increased, this seems unlikely to translate into significantly improved labour market outcomes in these regions in the near term. "If housing prices continue to decline in these locations, then banks may face additional losses on their mortgage portfolios."More broadly, the RBA applies a salve to burn applied in recent weeks by APRA, ASIC and itself over household indebtedness and lending standards."Improved lending standards in recent years are helping to keep the household debt-servicing burden contained." The RBA allows that "some evidence suggests that investor housing debt has historically performed better than owner-occupier housing debt in Australia, though this has not been tested in a severe downturn."Rather, the concern is that investors are likely to contribute to theamplification of the cycles in borrowing and housing prices, generating additional risks to the future health of the economy."While it is not possible to know what level of overall household indebtedness is sustainable, a highly indebted household sector is likely to be more sensitive to declines in income and wealth and may respond by reducing consumption sharply."