沙井 is the standard word for 'manhole' in Hong Kong and parts of Guangdong. In Mainland Mandarin, the more common term is 检查井 (jiǎnchájǐng) or 窨井 (yìnjǐng).
culture
There is also a town called 沙井 (Shājǐng) in Shenzhen's Bao'an district — historically known for oyster farming. Context disambiguates: street-safety = 'manhole', Shenzhen geography = 'Shajing town'.
