Water Sort

The tubes, and how you win

• Every tube holds 4 units of liquid.
• Each colour exists in exactly 4 units, and at the start those units are shuffled across the colour tubes.
• There are always 2 empty tubes, whatever the level. The number of tubes is the number of colours plus those 2.
• You win when every tube is either empty or full of a single colour.

The liquid is identified by colour alone — there is no symbol on the surface. Small shapes floating on the water were built and removed: they read as stickers rather than liquid. Two things make up for it. The palette keeps its 9 colours apart in both hue and lightness, and every tube can be read aloud as its colours from the bottom up, so the non-visual route does not depend on markings at all.

Pouring

• Tap a tube to pick it up, then tap another to pour into it.
• A pour is allowed when the source is not empty, the destination has room, and the destination is either empty or topped by the same colour as the source.
• What moves is the run of one colour on top of the source, as much of it as fits. Whatever does not fit stays where it was.
• A tap that does not meet those conditions does nothing at all. It is not a mistake to be punished, it is simply not a move.
• You can pour yourself into a dead end. That is not a flaw in the board — it is exactly why Undo and Hint exist and why neither of them is rationed.

Every board is proved solvable before you see it

Boards are not shuffled and handed over. The generator shuffles, then throws the result away unless it passes two checks, and only what survives both is ever dealt.

• A board that already contains a finished tube is discarded — you should not be given part of the answer.
• A solver then searches for a solution, and only a board it has actually solved becomes a candidate. If the search fails or is cut off, that attempt is thrown away and the next one is tried.
• It gathers 12 candidates, sorts them by how mixed they are, and picks the one at the position the level asked for.
• All of that runs from the level’s seed, retries included, so the same level always produces the same board.

How mixed a board is gets measured, not eyeballed: count the runs of a single colour on the board, and subtract the number of colours. One pour removes at most one run, and a finished board has exactly one run per colour, so that difference is a genuine lower bound on how many pours the board needs. Ranking candidates against each other also means no board is ever rejected for missing a threshold. The cost is one solver run per candidate — about 2 ms a board.

Moves, Undo and Hint

• One pour is one move, however much liquid it carried. Your move count is shown while you play.
• No clock is shown. The time is recorded and appears when you finish and in your statistics.
• Undo is unlimited and free. It steps back one pour at a time and rewinds the move count with it — you took the pour back, so the count goes back too.
• Hint is unlimited and free, and it is not a guess. The solver proves a solution from the position you are actually in, and the hint highlights the first pour of that solution — a move that provably finishes the board if you keep following it.
• When no solution comes back, the message says so plainly: no way forward was found, so undo or retry. It does not announce a dead end, because a search that was cut off and a board that is genuinely stuck look the same from the outside, and only one of them justifies that word.

How many hints you used is recorded and shown when you finish, as a fact about the run. It is never a cost, and there is nothing to watch or buy to get more of them.

The 100 levels

The level number decides the number of colours and how mixed the start is. Levels unlock in order, every unlocked level can be replayed, and replaying gives you the same board.

• Inside a band, the climb is how mixed the start is. There are only seven colour counts, so without that every level in a band would be the same puzzle with a different seed.
• The first level of a band is its tidiest deal and the last is its most mixed one, moving evenly in between.
• Entering the next band adds a colour and resets the mixing to its tidiest — so the step up happens once, not twice at the same time.
• Your fewest moves and fastest time are kept for each level.

The daily puzzle

• One board a day, the same for every player.
• 6 colours every day, the middle of the level curve. No weekday is harder than another.
• How mixed it is, is fixed too, at the middle of the range — 0.5. Taking the first deal that came up would have created lucky days and unlucky ones, which is the same reason the colour count is fixed.
• The last 30 days stay open, so a day you missed is still there to play.
• No streak is counted or shown. Statistics keep which days you solved and in how many moves.

Questions people ask