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Water releases from Wivenhoe have been halted. So what's the status of south-east Queensland's major water supply?

The dam is currently at "full capacity". But it's not as simple as that. (Supplied: Seqwater)

SEQ Water has stopped releases from Wivenhoe Dam, more than a week after they commenced.

So does that mean Wivenhoe's full? How long will that water last? And how did it ever surpass 100 per cent capacity? 

Well, first things first, we'll soon be talking in megalitres, so to make sure we're all on the same page, it takes 1 million litres to make 1 megalitre.

Let's get back to it.

How did Wivenhoe just go well past 100 per cent capacity?

Yes, Wivenhoe Dam is now at the full supply level, something it hadn't reached since 2015.

In fact, only two weeks ago it was at 58 per cent capacity and in September it had fallen as low as 41.8 per cent.

But it's not quite as simple as that.

Wivenhoe is a dual-purpose dam: it provides 1,165,238 megalitres of drinking water storage as well as 1,967,000 megalitres of temporary flood space.

That's a grand total of 3.132 million megalitres.

So, when Seqwater says "full supply level", they're talking about drinking water. There's still another 1.9 million megalitres of water storage available.

That's how we saw figures like 180 per cent capacity during the floods.

But to make things even more confusing, Wivenhoe, like Somerset and North Pine, needs an upgrade and until that takes place, its capacity has been reduced.

A spokesperson for Seqwater said this is a safety precaution.

"The temporary full supply level is in place whilst our dam upgrade program is completed.

"This program is delivering upgrades at a number of Seqwater dams, to ensure ongoing safety and security of bulk water supply well into the future."

So while Wivenhoe is at the "full supply level", it's not quite at 100 per cent of drinking water storage. More like 90 per cent.

This morning the water is at 88.6 per cent of capacity.

How long does a full Wivenhoe last?

On average, a person will use 155L of water on any given day.

Wivenhoe only supplies 50 per cent of south-east Queensland's drinking water but, according to an Seqwater spokesperson, the downfall from the last two weeks alone will last a couple of years.

Raising Wivenhoe Dam

Queensland Minister for Water Glenn Butcher told ABC Radio Brisbane yesterday a detailed business case on Somerset Dam will inform any developments to Wivenhoe.

"Where we're at now, since 2017, moving forward, is to identify whether not only do we do the safety works and the upgrades to them but can we also at the same time raise either Somerset or Wivenhoe or both to make sure we've got extra capacity plus we have safe dams."

While there's no plan set in stone yet, we should know more in 12 months' time.

Did Wivenhoe actually do its job during the recent rain event?

Premier Annastacia Palaszczuk said last week that Wivenhoe had held back four Sydney Harbours worth of water during the floods.

"Wivenhoe has two purposes: to hold our drinking water … secondly, it does flood mitigation," she said.

"Flood mitigation means that it can actually have that extra capacity to have all of that extra water.

"In 2011, it was uncontrolled releases. What we're seeing now is, it is being managed and it's controlled releases.

"That means that the controlled releases will not have any further impact in terms of the height of the floodwaters."

The Premier was again defending the releases yesterday.

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