There has been a constant disagreement in my company about what should and shouldn't be a hidden line. I work for a swimming pool company. We design in ground swimming pools, hardscape and outdoor livings. My thought has been that since our main focus is the swimming pool, the waterline should be a solid and clearly visible line. Our coping, or cap, overhangs 1" into the pool and I show that as a hidden line. I know that for typical "cad standards" it would be the other way around, as it might be shown for cabinets for example. But for this type of work specifically, where everything is working off that waterline, doesn't it make sense that the waterline be a solid line and not hidden? And not only hidden, but also in a lighter color? I'm tired of going back and forth fighting this with someone that doesn't even know much about cad and drawings, so I thought I'd come on here and ask for opinions.

Depends on whether or not you are a purist.  Seems these days everyone wants to be "different".  The emphasis should be on the pool not the water that is going to go in it.

It's not really about being different. When I say the waterline, I'm talking about the shape of the pool. The line we use to pull the measurements to lay it out. The line the excavators look at when they go dig it out. We say waterline, which means the inside finished wall of the pool. The line we use to measure to the house foundation and property line to get approval from the city.

In that case I'd side with you since it is used as a reference for measurements.