Is There a Better Way to Illustrate Water on a Dungeon Map Than This?

[Circa 1976]

They don't need to be (and in the case of square gridded maps, probably should not be) perpendicular.

standard crosshatching patterns exist in both archtecture and heraldry.

In heraldry, dark blue is horizontal lines, sky blue (either bleu celeste or skye in blazonry) is usually hatched as offset dashed horizontal lines.
The broken lines of BCel are much easier to spot and don't hide the grid as badly.

Note that the standard tinctures for heraldric colors and their current conventional hatchings
Or (gold/yellow): dotted, rows offset (forms a trigrid of dots)
Argent (silver/white): plain field
Azure (medium to dark blue): horizontal
Gules (red): vertical
Purpure (purple): 45° rises to the right ////
Sable (black): vertical and horizontal
Vert (Green): 45° falls to the right \\\\
Murrey (mullbery/a purplish red) crossed 45° lines
Sanguine (blood red): horizontal crossed by 45° falling to the right
Tenne (orange tan): vertical crossed by 45° falling to the right

Engineering, machining, and architecture have hatching patterns that are not strictly straight lines.
Here's a list of architectual drawing hatchings:
Standard hatching styles for drawings
And a discussion of one standard for use in Autocad:
CAD Hatch |BS 8888 and BS 308 Hatch Patterns (click on the red lozenge to follow it)
A pdf catalog of materials hatchings:

https://www.dot.nd.gov/manuals/design/caddmanual/AppendixG.pdf

I'm too lazy to dig out my Fox-Davies' TAOH for proper cites, but I've personally verified most of the hatchings against TAOH.
Hatching (heraldry) - Wikipedia (actually pretty decent, missing a couple rare colors - Carnation and gray... both of which are 18th C)

Hatching - Wikipedia

en.m.wikipedia.org

I checked out all the links. Now I believe I have a better understanding of the term. Thank you!

Funny thing; on that Standard Hatching Styles for Drawings page, they show an example of what is referred to as Aggregate style. When I first began drawing the map being discussed, I drew what I suppose is an aggregate hatching square, although I didn't know what it was called then, of course. While I try to include as much detail as I can in my maps, I sometimes find the actual labor thereof to be tedious. Using the square field I drew, when I need small amounts of rubble added to a feature, I can simply use the Selection tool in Adobe ID to choose as much as I need from this field, then copy and paste.

My 'aggregate' field:

Same graphic at 300% :

Used in the map (also at 300%):

 

[aramis erak]

I checked out all the links. Now I believe I have a better understanding of the term. Thank you!

You're most welcome.
It's worth noting that in heraldry, it's always lines and/or dots... being easy to draw with a dip pen.

Used in the map (also at 300%):
View attachment 381001

It's a great rubble effect!

 

[Cordwainer Fish]

Engineering, machining, and architecture have hatching patterns that are not strictly straight lines.
Here's a list of architectual drawing hatchings:
Standard hatching styles for drawings
And a discussion of one standard for use in Autocad:
CAD Hatch |BS 8888 and BS 308 Hatch Patterns (click on the red lozenge to follow it)
A pdf catalog of materials hatchings:
https://www.dot.nd.gov/manuals/design/caddmanual/AppendixG.pdf

Nifty. Can you get those in zipatone?

 

[Edgar Ironpelt]

Sure thing. Whenever I create a map symbol, even if I don't use it I still save it on the pasteboard outside the document.
View attachment 380883
The right side of the map is kinda blank, since it's a WIP.

I'd use non-cresting/peaking waves or wavy lines for water on a dungeon scale, along with shading. Here's a crop from one of my maps where a water wells out of a, well, well, and flows off in a rapid stream, at the 1 square = 5 ft scale.

 

[aramis erak]

Nifty. Can you get those in zipatone?

Some, most certainly, were available in zipatone.

One draftsman my dad worked with had rubber stamps, about 3x5 inches, with about 0.05 inch lines, in both solid, dotted, and alternating. He used them with stencils for the same effect. (CEn Sqdn Christmas party around 1982)
Gives me an idea: a roller with lines... stencil off the area to be halftoned, then roller over it with a rolling stamp...