The name comes from 滑水, 'sliding on water,' local slang for taking it easy. Ningxia Waterslide Mahjong is an easygoing variant that plays exactly like it sounds.
Before each hand starts, you swap three tiles with another player. That's the 'Change Three' (换三张) in Wanzhou Mahjong, and it completely changes how you plan your opening.
Zhengzhou Mahjong has a pre-round side bet that raises the stakes before the first tile is even drawn. Rewards self-drawn wins and fast hands built around wildcards.
Taiyuan's variant is called 'Standing Four' (立四), from Shanxi Province. Not Shaanxi. The name refers to a specific tile formation rule that defines how you build your hand here.
Yuxi Mahjong is named for how often you draw a bonus tile right after forming a Kong. Kong on Flower, 杠上花. Big hands happen more often than you'd expect here.