How Much Is a Megalitre? Volume, Value and What It Irrigates

The definition

A megalitre is one million litres. Written as ML, it is the standard unit of Australia's water market — every allocation account, entitlement volume and traded parcel is denominated in it.

The useful equivalences:

1 megalitre equals
Litres	1,000,000 L
Kilolitres (the unit on a water bill)	1,000 kL
Cubic metres	1,000 m³
As a cube	10 m × 10 m × 10 m
Over one hectare	100 mm of applied water

Scale up and you get the storage unit: a gigalitre (GL) is 1,000 ML — one billion litres. Seasonal allocations are announced against systems holding thousands of gigalitres; farm trades happen in tens or hundreds of megalitres. Same water, three prefixes.

What a megalitre looks like

About 40% of an Olympic swimming pool. A competition pool (50 m × 25 m × 2 m minimum depth) holds roughly 2,500 m³ — about 2.5 ML. So a megalitre fills a bit less than half of one.

Five to six households' water for a year. The average Australian household used 174 kilolitres in 2023–24 on ABS figures. A megalitre — 1,000 kL — is what five to six typical homes put through their taps, showers and gardens in a full year.

100 millimetres over a hectare. This one is exact, and it is the conversion irrigators live by: 1 ML spread across 1 hectare is 0.1 metres — 100 mm — of water. If a crop needs the equivalent of 1,000 mm of water in a season and rainfall supplies 400 mm, the balance is 6 ML/ha of irrigation.

What a megalitre irrigates

Seasonal water requirements vary with soil, system and season, but industry benchmarks for the southern Murray-Darling Basin cluster in well-established ranges:

Crop	Typical seasonal irrigation
Mature almonds	12–14 ML/ha
Citrus	10–12 ML/ha
Perennial dairy pasture (northern VIC)	8–12 ML/ha, system and season dependent
Wine grapes (Sunraysia/Riverland)	7.5–9 ML/ha

Read the table from the bottom up and you see the market's demand structure. A hectare of wine grapes needs roughly 8 ML; a hectare of mature almonds needs roughly 13 ML — and almonds cannot skip a year. That is why permanent horticulture anchors demand for water in dry seasons, and why prices firm the way they do when allocations tighten. The 10-year price history shows that mechanism playing out season after season.

For a dairy operation, one megalitre keeps roughly a tenth of a hectare of perennial pasture fully watered for a season. For an almond orchard, 1,000 ML — a gigalitre — waters about 75 hectares.

The storage scale

The same unit, three orders of magnitude up, describes the dams that supply the system:

• Lake Eildon holds about 3,334 GL when full — 3.3 million megalitres, the storage behind most of the Goulburn system's supply.
• Hume Dam holds about 3,005 GL — the Murray system's key regulating storage, roughly six Sydney Harbours (the informal "Sydharb" unit is 500 GL).

When a seasonal determination moves allocation by a few per cent, it is signalling a change in expected supply measured in tens of gigalitres — tens of thousands of megalitres — across the system. That is the supply side of the price you pay per megalitre.

What a megalitre is worth

The second meaning of "how much is a megalitre" is the one that matters commercially: the price.

Temporary water — allocation traded for use this season — is quoted in dollars per megalitre, and the range is wide. Across the last decade in Zone 1A (Greater Goulburn), season-average allocation prices have run from $36/ML in the wettest year to $485/ML in the depths of drought. Where the price sits inside that range at any moment is a function of storages, seasonal determinations, carryover and demand from permanent plantings — the full mechanics are in our price history, and current recorded trade prices by zone are on our water prices page.

Permanent water — the entitlement itself, which produces allocation every year — is also priced per megalitre but at entirely different levels, in the thousands of dollars per ML for high-reliability shares. One number is the price of this season's water; the other is the price of the asset that yields it. If that distinction is new to you, start with entitlements vs allocations.

Two rules of thumb keep the numbers honest when you are weighing up a trade:

• Per hectare, not per megalitre. Water at $300/ML sounds abstract; $2,400/ha to finish a wine grape crop, or roughly $3,900/ha to keep mature almonds alive, is a farm business decision.
• Compare against your marginal return. A megalitre is worth buying when the production it supports returns more than the water costs. In dry years, the growers still buying at $400+/ML are the ones whose crop losses would cost far more.

Why the unit matters when you trade

Everything in the Victorian system is accounted in megalitres: your water share's volume, the seasonal allocation credited against it, the balance in your allocation bank account, the parcel size on a trade application, and the price you disclose. There is no ambiguity in the unit — which means there is no excuse for ambiguity in a quote. When you are offered water "at market", the only two questions that matter are: how many megalitres, and at what price per megalitre.

For how those trades actually move between accounts, see how water trading works in Australia — or call the desk on (03) 5824 3833 and we will price the volume you need against today's market.