Water Tanks Solver

Water Tanks Solver — Step by Step

Drag across squares to join them into a tank, click a count outside the grid and type it, then press Solve. Or play a generated puzzle and send it here with one click.

Water Tanks Solver: rules, how to use it, tips

Fill tanks with water that lies flat and settles at the bottom, so every row and column has the right number of filled squares.

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.

Using the 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.

Tips

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.

The full guide, with a worked example and common mistakes: How to play Water Tanks.

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.