Aquarium is a logic puzzle about filling tanks with water. The numbers beside the grid say how many squares in each row and column hold water, and water lies flat: each tank fills from its bottom up, level all the way across. Work out how high each tank is filled.
The rules
Fill squares with water so that:
- Every row and every column holds as many water squares as its number.
- Water lies flat. If a square in a tank holds water, so does every square of that tank on the same row, and on every row below it.
So each tank is filled to one level: empty, full, or anywhere in between. You can also mark squares you know are dry.
Water lies flat
Here, the tank down the left holds water in its lower square, the 2×2 tank on the right is empty, and the bottom tank is full. In each one, the water is level and starts from the bottom.
What breaks a rule
Water above a dry square. Water would run down, so a tank can’t have water on top of a dry square:
Water not level across a tank. On any row, a tank’s squares are either all water or all dry:
The wrong amount of water in a line. The bottom row here is numbered 2, but holds three water squares:
In the game, a row or column number turns red when it can’t be met, and teal once it is. Water can’t be put in the wrong shape at all: tapping a square fills its tank level, from that row down.
A puzzle from the game, solved
This is Easy level 3 from the game, a 6×6 with 9 tanks.
It takes 11 steps. Here are the first four.
Steps 1 and 2: the 0 and the 6
Row 1 is numbered 0, so every square in it is dry. Row 6 is numbered 6, so every square in it holds water.
Step 3: just enough room
Column 1 is numbered 5. Its top square is dry (it’s in row 1), which leaves exactly five squares. All five hold water.
Step 4: water lies flat
Row 2, column 1 holds water, and it belongs to the tall tank on the left. Water lies flat, so the tank’s square beside it on row 2 holds water too, and so does everything in the tank below.
The rest
The same two ideas finish it. In all, it takes 7 steps from rows and columns that are finished or have just enough room, and 4 from water lying flat.
Where to start in any puzzle
Look for a row or column numbered 0, which is all dry, or numbered with its full length, which is all water. 101 of the game’s 150 levels have one: 44 of the 50 Easy levels, 35 Medium and 22 Hard. When there isn’t one, look for a small number crossed by a tall tank: water high in the tank would run down and overfill the line. Of the 49 levels without a 0 or a full line, 45 start that way.
Common mix-ups
- Water spreads across a tank, not just down. A tank’s squares on the same row are always alike.
- Tanks don’t share water. Two tanks side by side are filled separately, to their own levels.
- Dry only spreads up. Below a dry square, the same tank can still hold water.