How to play
Water Sort
Also known as Water Sort Puzzle, Water Color Sort, Color Water Sort, Liquid Sort Puzzle
- 1M+ downloads
- On Google Play since 2021
- Free to play
What is Water Sort?
Water Sort is a logic puzzle played with a rack of test tubes filled with layers of coloured liquid in scrambled order. You pour the top layer of one tube into another, and a pour is only legal when the colours match or the destination is empty. There is no timer, no randomness and nothing hidden - everything you need to solve the board is visible from the first move.
How to play Water Sort
Setting up the board
You start with a rack of tubes, most of them filled to capacity with coloured layers in random order, plus one or two empty tubes. Capacity is usually four units, and every colour appears exactly enough times to fill one tube completely. Later levels add more colours and more tubes rather than changing the rules.
How it works
- Tap a tube to lift it, then tap a second tube to pour into it.
- Only the topmost colour of a tube can be poured; layers underneath are locked until it moves.
- A pour is legal only if the destination is empty or its top colour matches the colour being poured.
- The destination must have free space - you cannot pour into a full tube.
- All touching units of the same colour on top move together; if the destination cannot fit them all, only as many as fit are poured.
- Nothing is ever added or removed and colours never change - you can only rearrange what is on the board.
- Undo reverses your last pour, subject to whatever limit the level sets.
How to solve
The level is solved when every tube either holds a single colour filling it completely or is entirely empty. No mixed tube may remain.
Solving tips
- Free one empty tube early and guard it. An empty tube is the only destination that accepts any colour, so it is the only tool you have for breaking a stack apart - spending it carelessly is the most common way to lock a board.
- Count before you pour. For each colour, work out how many units exist and how many separate places they sit in. The colour split across the fewest tubes is the cheapest to finish, and completing it frees a whole tube.
- Never pour into a nearly-full tube unless it completes the colour. A tube with three of four slots used can only ever accept one more unit; putting the wrong colour there wastes the slot and buries whatever sits beneath it.
- Merge, never split. Prefer pours that join a run onto a matching run, and avoid pours that leave part of a stack behind because the destination ran out of room.
- Look one move ahead at what a pour exposes. Before committing, check the colour underneath: if it will have nowhere legal to go, the move is a trap.
About this puzzle
Water Sort is a modern mobile puzzle genre rather than a traditional game, and it has no single documented inventor.
Colour-sorting tube puzzles spread rapidly across iOS and Android in 2019 and 2020, followed by hundreds of near-identical versions.
The mechanic itself is a visual dressing of a much older idea in computer science: rearranging items between limited stacks until each stack is uniform, the same family that includes Tower of Hanoi style and container-restacking problems.
Researchers have since studied it formally - a 2022 paper, Sorting Balls and Water, proved the general problem NP-complete and showed the liquid and ball versions are equivalent in solvability.
Frequently asked questions
Nothing is lost - there is no fail state, so you cannot lose a level, you can only reach a position where no useful pour is available. Undo back to the last real decision point, or restart the level, which costs nothing but time.
Levels in a released game are normally generated from an already-solved state, so a solution exists when the board loads. Your own moves can still make it unsolvable, though, because pouring a colour onto the wrong tube buries units permanently until you undo.
It adds one more empty tube to the rack for the rest of that level, giving you additional working space. Since an empty tube is the only place any colour can go, one extra tube often rescues a position that is otherwise locked - so save it for genuinely stuck boards.
A pour needs two things at once: the destination must be empty or topped by the same colour, and it must have room left. If tapping does nothing, one of those two conditions has failed.
Skill. The entire board is visible from the first move, there is no hidden information and nothing is randomised after the level loads, so every dead end traces back to a choice. Counting colours and looking one move ahead measurably improves your clear rate.
