Give a paranoid confirmation prompt when the player is levitating or flying over a liquid and attempts to remove an item that would result in them losing that levitation or flying and falling in.

New “flooded stairs” terrain type. They act normally as stairs, but are also treated as three-dimensional water (that you cannot fly over and must be submerged in, like on the Plane of Water). This would not be very useful on its own but would be a building block for quests or other special levels that are entirely underwater.

Water elementals’ HP (and Pw, if applicable) regeneration is boosted when they are on a water-containing space such as a moat or a fountain. Possibly, they can also suck up the water to regain a large quantity of hit points at once, which removes the water terrain if it is expendable (a fountain or pool or puddle of shallow water will dry up).

In order to make them more interesting in combat, their AI may favor hanging around sources of water and trying to find a path to the nearest water when they are injured.

The “Construction Patch”:

• When digging out stone (not necessarily walls) with a pick, rocks may fall on your head with a lowish chance, about 10% per dug square. These deal the least damage if you are wearing a dwarven helm, and a little less than normal if you are wearing some other hard helm. Dwarvish characters have a high chance of dodging the falling debris entirely. Possibly also allow a boulder falling on your head from digging similar to when monsters tunnel.
• You can apply rocks at an adjacent floor square to build a wall. It takes 50 rocks, or 25 if there is a boulder in that square. (If the space is marked as being wall-nondiggable, this either doesn’t work, or flips the space to being diggable.) It takes 1 turn per rock to build it. In the process it creates an immovable object or dungeon feature called “partially-built wall” on that space, which tracks how many rocks are part of it. If you move onto the space, you can dismantle the wall and retrieve the rocks.
• You can apply rocks at an adjacent pool or moat to attempt to fill it. The more rocks, the higher the chance of filling it. This takes only 1 turn.
• Stone to fleshing diggable wall turns it into huge chunks of meat.
• Force bolts from striking wands or the spell scatter rocks off diggable walls they hit, and in roughly 5 shots the wall is destroyed.
• Digging a pit or hole puts a pile of rocks on a random adjacent square.
• When you dig a hole and fall down to the next level, you are usually accompanied by a shower of rocks falling on and around you. Dwarves are more adept at dodging and getting hit by fewer rocks.
• When using a pick to dig a square of natural stone where the four orthogonally adjacent squares are all dug out already, you are asked if you want to carve out a boulder. If you say yes, a boulder is deposited on the new space.

Note that the two boulder-creation methods above run the risk of being exploited for abusable quantities of food if you have stone to flesh available, and the stone-to-flesh-walls method explicitly invokes this.

Pits created by freezing water and then digging out the ice gradually and randomly fill back in with water. But if you then try to frost walk on them (with water walking boots and white dragon scale mail), you get the following: “The water crackles and freezes under your weight. The ice breaks under your weight! You fall into your pit!” creating the pit anew on the space.

Artifact sapphire Ice-9. When it is dropped into water, it freezes the square and all adjacent squares into ice, and remains on top of the new ice.

Artifact whose main purpose is to soak up water and apply it to other things. It removes a pool or moat square or dries up a fountain when applied to one (moats may refill), gaining a charge each time. You can apply it to spend a charge blanking a scroll, erasing an engraving (any type, not just dust), cleaning your face or hands, and extinguish fiery monsters such as a flaming sphere (possibly instakilling them).

The initial idea was to create a “sponge” object as the base item type, but since it’s undesirable to make a new object just to be the base of an artifact, it could instead either be a “spongestone” gem, or just an artifact towel, since towels can already soak up water. (If implemented as a towel, the towel would only gain one charge of wetness when immersed in water, and could attempt to dry up that square immediately.)

Water walking boots do not sink in water. They stay on top of the surface and can be picked up by something else that has water walking.

Force-fighting a monsterless pool of water or moat or perhaps even lava while wielding Frost Brand should freeze that square into ice (or ground if it was lava).

Diluting a potion of amnesia in a water source turns the water into Lethe water. It prints “Dark clouds roil beneath the water’s surface”, or “Somebody’s poisoned the water hole!” if hallucinating.

Fire and frost horns, rather than shooting a bouncable ray of fire or cold, cause a powerful area fire or frost effect centered on you. The intensity diminishes the farther away from you it gets, but it hits every single creature in its fairly large radius (except you).

This effect could also freeze water and lava or evaporate pools in the radius of effect as well.

When you fall into water, you can choose the adjacent space you climb out on.

Water turbulence won’t affect your underwater movements unless you are trying to move from one water square to another water square, and the water square you are on has at least one orthogonally adjacent water square.

Option to invert the colors of liquids, so the dominant color of the character glyph is the liquid color.

If you fall into water with teleport-at-will, the game should use casting a teleport spell as its last resort, once you have no other options for escape. It’s very annoying to attempt to teleport and lose energy and nutrition when you’re deliberately trying to jump in the water and can easily climb right back out.

Allow the player to dip into adjacent pools, as this is not actually hard to do in real life.

Sokoban levels with water or lava instead of holes (and make it so that boulders never sink without a trace in Sokoban). Air currents will still pull you down into the liquid if you try to go over them. Not specified what should happen if the player tries to boil away or freeze the liquids.

Using fire on the water on the Plane of Water boils the water away and opens up air space, but spawns in steam vortices.

A Mines’ End that has a water theme, though not necessarily as extreme as the Gnomish Sewer.

If there is a web over water or lava and you are a web-walking monster, you can move onto that space without falling into the liquid. Possibly if you’re any monster, not just a web walker.

Piranhas and other sea monsters’ bite attacks can only hit you if you’re actually in the water, in a water space next to them.

Water nymphs may create a pool on their spot when killed. Items they stole from the player fall into it, of course.

Wood nymphs may create a tree on their spot when killed, and mountain nymphs may leave a boulder.

Object property “frost walker”, which only generates on boots. When worn, lava cools into solid floor and water freezes into ice in a radius 1 around the wearer. Optional if they unfreeze afterwards. Alternatively, make this an artifact pair of water walking boots.

More harassment effects: the chance of respawning the Wizard is a fixed 1/7 and the rest of the effects are equal probability. Multiple non-duplicate effects may happen at the same time.

• Unchanged: curse items, summon nasties, vaguely nervous, aggravate monsters
• Darken much of the level, and extinguish, destroy, or cut the remaining lifetime of light sources. Maybe also blind the player.
• Drop boulders around the upstairs, or iron bars.
• Spawn pools centered on the player, with sea monsters in them.
• Spawn lava around the level, not under the player.
• Create a hole or pit under the player.
• Create a stinking cloud centered on the player.
• If you are carrying the Amulet, it teleports to a random square on your level or the level below.
• If you are carrying the Amulet, it (and possibly any fake Amulets) becomes heavier. This either lasts until the next harassment triggers, or is permanent but the total amount of weight added to the amulet has some sort of cap on it. This is interesting primarily because it targets carry cap, which is a valuable end-game resource.
• A variety of powerful player debuffs such as dealing half damage, taking double damage, blocking HP or Pw regeneration, super hunger, etc.

Saltwater or murky water, intended as a nerf for “just dilute most potions”:

• Potions of saltwater behave exactly like potions of water, except that they cannot be used to bless or curse things. Holy (and unholy) water must be pure.
• All in-game sources of water except for magic fountains (possibly regular fountains as well, but they might be too plentiful) are saltwater. Diluting potions in them will yield only potions of saltwater.
• Can also get pure water if a unicorn horn dip would already result in water.
• Not specified what cancelling potions should do. Possibly most potions just cancel to saltwater, juice or sickness. It’s weird because flavor-wise it shouldn’t produce anything but pure water, but it obviously won’t fix the current problem if you merely have to cancel potions instead of diluting them.
• If called murky water instead of saltwater, the “murky” randomized potion appearance should change.

Alternatively, don’t actually make saltwater a separate potion; just use saltwater as a flavor reason for why the player can’t intentionally dilute potions to water. (Can use a separate flavor argument, that potions are generally corked while not used, to explain away the lack of dilution for water damage.) Also, make most potions cancel into non-water base potions (such as confusion and hallucination to booze), with the notable exception of polymorph. It’s also harder or impossible to get water from random alchemy or polymorph.

A third option is naming blessing-capable potions “purified water” and leaving the mundane potion of water as it is. Things such as unicorn horns can neutralize toxins but can’t actually remove them, so the resulting water isn’t purified.

H-class monsters are tall enough to stand above water, and don’t drown in it. Or maybe they only drown on water spaces completely surrounded by other water.

Throwing a cockatrice corpse into water turns it into a hard floor, or possibly ice, with the corpse buried in the new floor.