The board
- A level is a set of bottles, each with a capacity of four units of liquid.
- Every colour in the level appears exactly four times, which means each colour fills exactly one bottle when it is finished.
- Some bottles start empty. The number of empty bottles is what mainly controls difficulty: two spares is comfortable, one spare is hard.
- Nothing is hidden. The whole board is visible before your first move.
The one rule that matters
A pour is legal when both of these are true:
- The target bottle is empty, or the colour on top of it matches the colour you are pouring.
- The target bottle has at least one free unit of space.
Everything else follows from that. There is no rule about how many units you must move, no rule about which bottle you start from, and no limit on the number of pours.
What happens during a pour
- Only the top block of identical colour can move. If a bottle holds pink, pink, green from the bottom, only the green is available.
- The whole block moves if it fits. Three green units pour into a bottle with three free units in a single action.
- If the block does not fit, as much as fits moves and the rest stays. This is a partial pour, and it is legal — but it splits a colour across two bottles, which usually costs you moves later.
- Liquid never mixes into a new colour and never disappears. The total amount of each colour is constant.
Illegal pours
| Attempt | Why it is refused |
|---|---|
| Pouring yellow onto green | Colours must match unless the target is empty. |
| Pouring into a full bottle | Four units is the hard ceiling. |
| Pouring from an empty bottle | There is nothing on top to move. |
| Pouring from the middle of a bottle | Only the top block is reachable — this is the core constraint of the game. |
| Pouring a finished bottle into an empty one | Physically legal but always harmful, so the game on this site blocks it to protect your progress. |
Completed bottles
A bottle with four units of the same colour is finished. Nothing in the rules forces you to leave it alone, but there is never a reason to touch it: emptying it back out cannot expose anything new, because everything underneath is the same colour. Treat a completed bottle as removed from the puzzle.
Empty bottles
An empty bottle is the only place that accepts any colour. That makes it the most valuable square on the board, and the moment you drop one unit into it, it becomes a bottle that accepts one specific colour instead. This is why experienced players talk about "free space" rather than "empty bottles" — what matters is how many free units you have and how many different colours can use them.
Deadlock: when a board is stuck
A position is deadlocked when no legal pour exists: every non-empty bottle has a top colour that does not match any other bottle's top colour, and no bottle is empty. It can also be effectively lost while legal moves still exist — you can shuffle liquid around but never isolate a colour.
Starting positions on this site are always solvable, because a solver verifies them before they load. A deadlock is therefore always the result of pours made during play, and the remedy is undo, the extra bottle, or a restart. See solving difficult levels for how to spot the danger a few moves early.
How a level ends
The level is complete when every bottle is either empty or filled with four units of one colour. There is no scoring, no star rating and no move limit on this site — a solution in forty pours counts the same as one in twenty. If you want the extra challenge, try to match the shortest line you can find and use the hint afterwards to compare.