Sometimes certain meshes can make one's computer software lag dependin' on a variety of factors. This is solely why in the public maps, there isn't an overload of meshes as too many meshes contributes to said factors. When in yer own map, I advise ye' turn yer water reflection off and lower yer view distance. In addition, switchin' yer renderin' mode can also aid in calmin' down that lag.
My apologies if my post was brief. I'm currently on my phone so if ye' need a clearer explanation, feel free to inform me.
If you were working on your map in map maker at that moment, the lag would not be caused by the server.
It depends if you were experiencing such lag as fps lag, where the whole game feels laggy.
Or if it was such as server lag, where there is a few seconds delay on everything you do.
Such as placing meches and opening windows.
As Vespian mentioned, turning the water off can reduce lag.
But it's at the same time important to make sure the map isn't too laggy with it switched on.
It's usually up to the graphics on your computer, if there's FPS lag.
You could make sure to keep an eye on how many programs you're running in the background.
Ping lag is usually caused by downloading, or if the server is experiencing some issues.
(Which is why I usually check with friends icase they're experiencing lag as well, before restarting my router. )