Kenya has undergone rapid urbanization as people migrate to the cities in search of economic opportunities. This has given rise to informal settlements characterized by overcrowding, poor infrastructure, and inadequate social amenities. A cross-sectional study on water, sanitation, and hygiene (WASH) status was carried out in Mathare, an informal settlement in Nairobi. A random sample of 380 households was used. The average household size was five people, and 26% of the household heads had completed secondary or higher level of education. The main source of income (70%) was self-employment with 41% of the households living on less than 1.5 USD per day. The WASH situation in the urban slums is below the minimum standard recommended by the World Health Organization (WHO). There is need to improve the situation by improving and installing basic infrastructure including water, sanitation, and solid waste collection.