How to play Water Jugs
Measure an exact amount of water using jugs with no markings — fill, empty and pour. Also known as Pouring puzzle.
The rules
- Each jug shows how much it holds when full. There are no other markings.
- With a tap you may fill a jug to the top, or empty it completely.
- You may pour one jug into another; the water stops when the first is empty or the second is full.
- Finish with exactly the amount shown in one jug — or, in Share it out, two jugs with half each.
Playing Water Jugs on Puzzle Solvers
- Choose a level and press New Puzzle. The goal is shown above the jugs.
- Use the Fill and Empty buttons under a jug to use the tap or tip it out.
- To pour, tap one jug and then another: water flows until the first is empty or the second is full.
- In Share it out there is no tap — just pour until two jugs hold half each. Hint explains the next step of the shortest plan.
A worked example
Jugs of 3 L and 5 L, target 4 L. Fill the 5 L and pour into the 3 L: 2 L stay in the 5 L.
Empty the 3 L, pour the 2 L into it, fill the 5 L again and top up the 3 L — that takes 1 L, leaving 4 L in the big jug.
Strategies
- Remainders measure. Pouring a full big jug into a small one leaves big − small behind.
- Fill, pour, empty, repeat. Keep filling one jug and pouring it into the other, emptying the other when it is full. The amounts left behind step through every possibility.
- Try both directions. Filling the small jug and pouring into the big one gives a different sequence — one of the two is usually shorter.
- Work backwards. Ask what you need just before the end: often a full jug with exactly the right gap in another.
Common mistakes
- Emptying a jug that holds an amount you need.
- Pouring back and forth between the same two jugs without making progress.
Where it comes from
Pouring puzzles appear in mathematical recreations going back to the Middle Ages, and the 3-and-5-litre version became famous in films and maths classrooms alike.
Frequently asked questions
Is every target possible?
Every puzzle here can be solved; the counter shows the fewest moves needed.
Does pouring count as one move?
Yes — fill, empty and each pour are one move each.
What is Share it out?
There is no tap: one jug starts full and you must split it into two equal halves by pouring between the jugs.
Keep going
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All guides: How to play every puzzle and game.