Nairobi Estates at Risk Due to Increasing Use of Borehole Water Water Vendors Suppling water Using Jerrycans File Residents in a number of estates in Nairobi have been warned over the long-term effects of borehole water that are being drilled in the county at an alarming rate, according to experts. Data shows that in Nairobi County there are four thousand registered boreholes. Embakasi, Kyuna, Karen, Loresho, Muthaiga, Upper Parklands, Langata and Spring Valley have the highest number of boreholes in the county. The World Health Organization(WHO) in its guidelines on salt in drinking water - mostly found in borehole water - says that if salt is excessive or above two grams per day, it may be harmful.