How many litres of water to cook pasta?
The famous rule is 1 litre per 100 grams — five litres for a 500g packet. It works, but it's a dilution rule, not a law of physics. You can cook the same pasta to the same al dente in roughly a third of that water, even starting from cold — and the more concentrated starch makes a better sauce.
The pasta pot
drag the amount — the pot fillsThe "rule" and the amount you can actually get away with — side by side, in a pot that grows as you add pasta.
Add about 20 g of salt (10 g per litre). Spaghetti takes roughly 9–11 minutes. The low-water figure is the cold-start method tested by Harold McGee and America's Test Kitchen — same al dente result, far less energy.
Low-water cooking needs more stirring in the first two minutes, and isn't recommended for fresh or filled pasta.
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The rule is really about dilution
As pasta cooks it sheds starch. The "1 litre per 100 g" convention exists to dilute that starch enough that the strands don't glue together, and to give the pot enough thermal mass that it doesn't stop boiling the instant cold pasta hits it. Both problems are real — but both have other solutions. Dilute less and stir more, and you reach exactly the same place. The rule isn't sacred; it's the lazy way to avoid stirring.
The rule you're allowed to break
In his February 2009 Curious Cook column for the New York Times, food scientist Harold McGee argued you can drop a pound of pasta into as little as 1.5 quarts (~1.5 L) — or even start it in cold water — and save most of the energy normally spent heating a giant pot. America's Test Kitchen ran the experiment and went further: 1 pound of dried pasta started in 1 quart of cold water came out just as al dente as the same pasta in four quarts of boiling water, with only the most sensitive tasters spotting any difference — and total cooking time fell by up to 45%. J. Kenji López-Alt and Alton Brown have reached the same conclusion. The catch: stir more in the first couple of minutes, and skip it for fresh or filled pasta.
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"Salty like the sea" is an exaggeration
The instruction to make pasta water "salty like the sea" is a good vibe and a bad measurement. Average seawater carries about 35 grams of salt per litre; the kitchen norm of 10 g/L is less than a third of that. Hit true seawater salinity and most sauces tip into inedible. Ten grams a litre gives you water that tastes pleasantly seasoned — enough to flavour the pasta from the inside as it absorbs water, without wrecking what you toss it with.
Oil is a myth; the starchy water is the real tool
Olive oil in the boiling water does nothing useful: oil and water don't mix, so it floats, then coats the pasta as you drain — the opposite of what you want, because sauce now slides off. The actual tool is the cloudy water you're about to pour away. Its dissolved starch is an emulsifier; a splash tossed vigorously into grated Pecorino and pepper turns cacio e pepe glossy instead of clumpy, and does the same for carbonara and aglio e olio. Cook in less water and that starch is more concentrated — another quiet argument for breaking the five-litre rule.
Frequently asked
How much water do I need to cook pasta?
The traditional Italian rule is 1 litre of water per 100 grams of dried pasta, so 5 litres for a 500g packet. But that is more than you actually need — tests by Harold McGee and America's Test Kitchen show pasta cooks just as well in roughly a third of that, even started in cold water.
Can I really cook pasta in less water?
Yes. America's Test Kitchen cooked 1 pound of dried pasta in 1 quart of cold-start water and got the same al dente result as 4 quarts of boiling water. It saves water and energy and cuts total cooking time by up to 45%. Stir more in the first two minutes, and don't use it for fresh or filled pasta.
Should I add oil to pasta water?
No. Oil floats on the surface and coats the pasta as you drain it, which stops your sauce from clinging. It does nothing to prevent sticking — plenty of water and a stir does that.
How much salt should I add to pasta water?
About 10 grams (roughly 1.5 teaspoons of fine salt) per litre. The phrase 'salty like the sea' overstates it — real seawater is about 35 g/L, more than three times that.
Why should I save the pasta water?
The starch dissolved in it is an emulsifier. A splash binds fat and water into a glossy sauce — it's what makes cacio e pepe and carbonara work instead of splitting into a greasy, clumpy mess. Using less water makes that starch more concentrated.
Sources
- Harold McGee — The Curious Cook, New York Times, 25 February 2009: cooking pasta in far less water (≈1.5 quarts/lb) and from a cold start.
- America's Test Kitchen / Cook's Illustrated — cold-start test: 1 lb dried pasta in 1 quart cold water, al dente, up to 45% less total time (not for fresh/filled pasta).
- J. Kenji López-Alt (Serious Eats) and Alton Brown — independent confirmations of the low-water / cold-start method.
- Traditional convention: 1 litre water per 100 g dried pasta; ~10 g salt per litre.
- Average seawater salinity ≈ 35 g per litre (oceanographic standard) — context for "salty like the sea".
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Related
Five litres is the tradition. A third of that, a bit more stirring, and a saved cup of the cloudy gold is the better answer.