Meaning:
“自” means “self,” “来” means “coming,” and “水” means “water.” This term, which literally means “tap water,” was perhaps first coined to express people’s wonder and joy towards the convenience of tap water. However, Chinese netizens who have given it a new meaning use “水” as a short form of “水军,” which refers to people paid to post online promoting contents. Unlike paid online touters, “自来水” are those who help to spread the word out of their own will. The earliest use dated back to 2015, when a group of fans of the animation movie “Monkey King: Hero Is Back” called themselves by this moniker after being mocked as “paid touters.”
Example:
A: 这两天有部电影很火啊，据说全民自来水。
Zhèliǎngtiān yǒu bù diànyǐng hěn huǒ a，jùshuō quánmín zìláishuǐ。
A new movie has become a huge hit, as many fans are endorsing it online.
B: 最近天天看球，我都很久没看电影了。
Zuìjìn tiāntiān kàn qiú，wǒ dōu hěnjiǔ méi kàndiànyǐng le。
I’ve been watching World Cup games lately and haven’t been to the theater for a while.