Pipes — free pipe connecting puzzle, no download

Thirty-six pieces of pipe sit in a six-by-six grid, every one of them spun to a random angle. Tap a piece to rotate it a quarter turn. The puzzle is solved when every pipe joins the gold source and no end is left pointing at a wall or at nothing — one single network, no leaks and no strays. Pieces that have joined the network light up green as you work, so you can see the water spreading rather than guessing.

Each puzzle is built as a spanning tree — a network that already reaches every square exactly once — and only then are the pieces spun. That guarantees a solution exists and that it is unique in shape, so a puzzle you cannot finish is a puzzle you have not finished yet. Your score is the time on the clock. Free, instant, and it works the same on a phone.

How to play

• Tap a piece to turn it a quarter turn clockwise.
• Join every piece to the gold source in the middle. Joined pieces turn green.
• No end may point at a wall, and no end may point at a neighbour that does not point back.
• The clock is your score, so a fast tidy solve beats a slow lucky one.
• Every puzzle is generated as a spanning tree first, so a solution always exists.

Solve the edges first — the walls do half the work

The single most useful fact about this puzzle is that a pipe may never point off the board. That is not a rule you have to remember so much as a free constraint you can harvest. A straight piece sitting on the top row cannot be vertical, so it is horizontal — decided, without looking at anything else. An elbow in the top-left corner has only one legal rotation of the four. A T-piece on an edge has exactly one. Work the border before you touch the middle and a surprising fraction of the grid fixes itself.

The second lever is the dead end. Single-armed pieces look like the least informative things on the board, but they are the opposite: a dead end has one arm and therefore exactly one neighbour it can feed from, so once you know which side its neighbour offers, its rotation is forced too. Chase each dead end back towards the middle and you tend to resolve a whole limb of the network in one pass.

What you should not do is rotate at random and watch for green. Because the network is a tree, a piece can be pointing perfectly correctly and still be grey — it simply has not been reached yet, because something between it and the source is wrong. Green tells you what is connected, not what is correct, and treating it as a correctness signal is the fastest way to undo work you had already got right. If you like constraint-chasing of this kind, Nonogram and Killer Sudoku are the same habit applied to numbers.

More games

More puzzles that always have a solution: Nonogram, Liquid Sort, Lights Out and Sokoban. Or browse all games.