How to play
- Goal
- Place oxygen atoms so every hydrogen belongs to one complete H2O molecule.
- How it ends
- A chart is solved when every hydrogen can be paired to exactly one oxygen, every oxygen has two hydrogen partners, and no two oxygens touch; there is no loss.
- Record
- The fastest first solve of each chart is kept as a public record, with its holder's name.
- The fixed H atoms are your clues. Place O in empty squares until every H belongs to exactly one O and every O has exactly two orthogonally neighbouring H partners. Both straight and bent H–O–H shapes are valid; no two O atoms may touch, even diagonally. The worked picture shows one straight molecule forming.
- Tap an empty square to place O; tap that O again to remove it. Tap a fixed H to highlight its neighbouring oxygen sites. No X or empty mark is needed.
- Undo reverses one placement or removal. Restart clears the oxygen marks but keeps the clock running. The chart completes automatically when every H and O can form valid molecules; there is no loss.
Controls
| Tap / click a blank square | Place an oxygen; tap it again to remove it |
|---|---|
| Tap a hydrogen | Highlight neighbouring oxygen sites |
| Arrow keys | Move focus through the chart |
| Space / Enter | Place or remove oxygen in the focused square |
| Z | Undo the last oxygen change |
| Escape | Close a panel or return to the atlas |
All 160 charts have stable IDs, one independently verified oxygen layout and hydrogen assignment. The private answer witnesses do not ship. Progress uses morass.h2o.v1. No ads or analytics run inside the game.
About H2O
At a rainmaker’s table in Orenvalt, silver hydrogen wisps wait for cobalt oxygen runes. Each oxygen bonds to two neighbouring hydrogens, turning the chart into water.
Explore 160 original charts from 5×5 through 8×8. Every chart has one independently proved answer, and oxygen runes must stay apart even at the corners.
Your first solve time is kept in this browser. An uninterrupted first solve may claim the public best shown beside the clock and on every chart card.
