*2.1. Study Area*

The primary source of water to support the daily needs of the majority of the population in Guinea-Bissau, including drinking water, are open/unprotected, shallow hand-dug wells (<15 m). Previous studies reported that about 80% of those water sources were contaminated with faecal materials and had an acidic pH [12,14]. Guinea-Bissau has a tropical climate (hot and humid), with a dry season (DS) spanning from November to May, and a wet season (WS) with high precipitation from June to October. The most representative soil groups in the country are Ferrallisols, Plinthosols, Gleysols, Fluvisols, and Arenosols [15].
