How to play Water Tanks
Fill tanks with water that lies flat and settles at the bottom, so every row and column has the right number of filled squares. Also known as Aquarium style puzzle, Water level puzzle.
The rules
- Thick walls divide the grid into tanks.
- Each tank is filled up to some level — or left empty. Below the level every square of the tank is filled; above it, none are.
- The level is the same right across a tank: squares of the same tank at the same height are either all filled or all empty.
- The numbers count the filled squares in each row and column.
Playing Water Tanks on Puzzle Solvers
- Choose a size and a difficulty, then press New Puzzle.
- With Water level, tap a square to fill its tank up to that height. Tap the top row of the water again to lower it.
- Mark empty dots squares you know stay dry; drag to dot several. Right-click also dots.
- Counts turn green when a row or column is right; Hint explains the next deduction.
Using the Water Tanks solver
- Choose the size, draw each tank and type the counts (or press Sample).
- Press Solve and step through: empty rows, rows where a tank fills together, and water settling to the bottom.
A worked example
Row 1 shows 0, so the top row is dry. A tank that sits only in rows 1 and 2 can have at most its row-2 squares filled.
Row 4 needs 2, and a tank has three squares in row 4 — so that tank stays dry at that height (and above), and the 2 must come from other tanks.
Strategies
- Dry rows. A row with 0 has no water — so nothing above it can be filled in any tank that reaches below it, either.
- Fill together. In a row, all the squares belonging to one tank go together. A row needing 3 can’t use a tank that has 4 squares in it.
- Bottom first. If a square is filled, everything below it in its tank is filled. If a square is dry, everything above it in its tank is dry.
- Full lines. A count equal to the length of its line fills every square — and the water below them in each tank.
- Columns. A column count limits how high each tank in it can fill.
Common mistakes
- Filling a square at the top of a tank while leaving a square below it dry.
- Filling only part of a tank’s squares in one row.
- Forgetting that the bottom of a tank may be in a different row in each column.
Where it comes from
Water-filling grid puzzles became popular in puzzle apps and magazines in the 2010s; they are a lovely mix of counting and simple physics.
Frequently asked questions
Can a tank be empty?
Yes — empty, partly full and full are all fine.
Does water flow between tanks?
No — each tank is separate, with its own level.
Is there always one answer?
Yes — every puzzle here is checked to have exactly one solution.
How do I solve one from a book?
Open the Water Tanks Solver, draw the tanks, type the counts and press Solve.
Keep going
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