Why does 牛车水 mean Chinatown?
牛车水 literally means 

牛车 - oxcart
水   - water


i.e. 牛车（运）水, oxcart (carrying) water. 


  牛车水（Chinatown）是新加坡的唐人街，名字的由来也反映了当年华人的一段历史。当时来南洋生活在这里的华人没有自来水用，于是用牛车运水，每天这里都是一辆辆的运水牛车，也算得上是车水马龙的壮观景象了。久而久之人们就称这里为牛车水了。


There's no tap water in the past, it was general to transport water by oxcart in chinatown, as time passes chinatown began to be called as 牛车水.