The what-if technique says: suppose a tank’s row holds water (or stays dry), and follow what that forces. If some row or column can no longer meet its number, it goes the other way. It’s the technique for when nothing simpler works anywhere.
This is the last of the Aquarium techniques. Each page shows its technique on the same 10×10 from the game, Hard level 16.
The rule
- Check that no simpler technique finds anything: no finished line, no flat water to spread, no too much water or no room, no line with only one arrangement.
- Pick a tank row, often one in a crowded line, and suppose it stays dry (or holds water).
- Follow what that forces with the other techniques.
- If a number turns out too high or out of reach, the supposition was wrong: mark the square the other way.
In a real puzzle
On the 10×10, it’s needed once, at step 26. Suppose the two squares at the left of row 2 stay dry. Following the counts from there, 14 moves later column 7 can’t reach its number. So they hold water.
The chain here is long; on paper you’d rarely follow one that far. In practice, try what-if on a tank row in a line that’s nearly finished, where a choice runs into trouble quickly.
How often you’ll need it
Never on Easy or Medium, and on 39 of the 50 Hard levels, 2.4 times per Hard level on average. On the 10×10 here it’s 1 of the 43 moves.