I have been investigating Haiti's water system since 2007 and strongly believe that the limited resources available to combat the country's cholera epidemic should be spent on sanitation and clean water, rather than on vaccination (Nature 469, 273–274; 2011). Otherwise, the local geology and ecology will allow cholera and other water-borne pathogens to persist.

Haiti has a backbone of granitic igneous rocks near the border with the Dominican Republic, surrounded by sedimentary limestone and shale. Fissures in limestone give rise to shallow aquifers that are especially prone to contamination by water-borne pathogens.

The devastation of last year's earthquake in Haiti joined intractable problems of poverty, deforestation and the loss of its microbiotic ecosystem. Soil microorganisms that consume pathogens are integral to the macrobiotic ecosystem, and are a first line of defence against groundwater contamination. The loss of Haiti's soils and the beneficial organisms they host means that many shallow aquifers are now unprotected.

Pathogens that thrive in Haiti's warm groundwater are flushed out by heavy rains and hurricanes, helping them to spread and cause new disease outbreaks. This is why funds should be spent on long-term, sustainable and resilient water resources.