The grim news this week is that the weakening in the economy continued for the third quarter in row, with economic activity needing to be propped up by government spending.

The Australian Bureau of Statistics’ “national accounts” showed real gross domestic product – the nation’s production of market goods and services – grew by just 0.3 per cent in the September quarter of last year, 0.2 per cent in the December quarter and now 0.4 per cent in the March quarter of this year, cutting the annual rate of growth down to 1.8 per cent.

Illustration: Matt Davidson

That compares with official estimates of our “potential” or possible growth rate of 2.75 per cent a year. It laughs at Treasurer Josh Frydenberg’s claim in the April budget – and Scott Morrison’s claim in the election campaign - to have returned the economy to “strong growth”, which will roll on for a decade without missing a beat.

It suggests Frydenberg’s boast of having achieved budget surpluses in the coming four financial years – and Labor’s boast that its surpluses would be bigger – are little more than wishful thinking, manufactured by a politicised Treasury.

The future may turn out to be golden but, even if it does, the econocrats have no way of knowing that in advance – they’re just guessing - and the road between now and then looks pretty rocky.

Why is the immediate outlook for the economy so weak and uncertain? Not primarily because of any great threat from abroad – though a flare-up in Donald Trump’s trade war with China could certainly make things worse – but primarily because of one big and well-known problem inside our economy: five years of weak growth in wages.

When you examine the national accounts, that’s what you find. Over the nine months to March, the income Australia’s households received from wages grew by 3.5 per cent, before adjusting for inflation.

That wasn’t because of strong growth in wage rates, but because more people had jobs. Weakness in other forms of household income meant that total household income grew by just 2.4 per cent.

But households’ payments of income tax grew by 4.5 per cent, thanks mainly to bracket creep. This helped cut the growth in household disposable income to 2 per cent. Even so, households’ spending on consumer goods and services grew by 2.2 per cent – meaning they had to reduce their rate of saving.

The result suggests the economy will grow much slower than anticipated in Treasurer Josh Frydenberg's April budget. AAP

Actually, the last big fall in households’ rate of saving occurred in the September quarter. Since then, households have tightened their belts, cutting the growth in their consumer spending so as to raise their rate of saving from 2.5 per cent of their disposable income to 2.8 per cent.

Reverting to “real” (inflation-adjusted) figures, this explains why consumer spending has grown by only about 0.3 per cent a quarter since June, reducing its growth over the year to March to an anaemic 1.8 per cent.

The bureau noted that the weakness in consumer spending was greatest in discretionary spending categories, including on recreation, cafes and restaurants, and clothing and footwear – a further sign that households are feeling the pinch.

Since consumer spending accounts for almost 60 per cent of GDP, that’s all the explanation you need as to why the economy’s now so weak. But there are other factors contributing.

One is the end of the housing boom. Home-building’s contribution to growth peaked in the September quarter, with building activity falling by 2.9 per cent and 2.5 per cent in the following two quarters. It will keep falling for some time yet.

And business investment is also weak. While non-mining investment grew by 2 per cent in the quarter, mining investment fell a further 1.8 per cent. Overall, business investment was up 0.6 per cent in the quarter, but down 1.3 per cent over the year to March.

External demand is helping, however. With the volume of exports growing, while the volume of imports was “flat to down” - another sign of weak domestic demand - “net exports” (exports minus imports) are contributing to growth.

Even so, total private sector demand (spending) has actually fallen for the second quarter in a row. So, apart from the contribution from net exports, any growth is coming from public sector demand.

It grew by 0.7 per cent in the quarter to be 5.5 per cent higher over the year. This reflects the rollout of the National Disability Insurance Scheme and state spending on infrastructure. It means government spending contributed half the growth in GDP during the quarter and more than 70 per cent of total GDP growth over the year to March.

Consumers have stopped spending on recreation, cafes and restaurants, and clothing and footwear – a further sign that households are feeling the pinch. Josh Robenstone

Note, it’s not a bad thing for government spending to be contributing to growth. That’s exactly what it should be doing when private demand is weak. No, the concern is not that public spending is strong, it’s that private spending is so weak.

Dividing GDP by the population shows that GDP per person fell fractionally for another quarter, and grew by a mere 0.1 per cent over the year to March.

This tells us not that the economy is on the edge of recession – how could GDP contract when a growing population is making it ever bigger? – but that, as Jo Masters of Ernst & Young has said, “growth is being driven by population growth alone, and not increased participation or productivity”.

The economy’s getting bigger, but it’s not leaving us any better off.

Speaking of productivity, the productivity of labour deteriorated by 0.5 per cent in the March quarter and by 1 per cent over the year.

Is this a terrible thing? Well, before you slit your wrists, remember that when employment is growing a lot faster than the growth in the economy would lead you to expect, a fall in GDP per worker (or, in this case, per hour worked) is just what the laws of arithmetic would lead you to expect.

Surprisingly strong growth in employment – most of it full-time – doesn’t sound like a bad thing to me. It’s just hard to see how it can last much longer.

Ross Gittins is the Herald’s economics editor.

Twitter: @1RossGittins