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The Northeast of Brazil, a semi-arid region, frequently experiences severe drought. Despite rainfall during two or three months of the year, the presence of soils with low water retention capacity, together with intense insolation, results in infiltration of water to deeper soil layers, rapid evaporation, and deficiency of water during the rest of the year. In this work, we propose the use of soil conditioners derived from agricultural and industrial wastes to improve soil water supply. Five biochars, prepared by slow pyrolysis, were produced from green coconut shells, orange peel, palm oil bunch, sugarcane bagasse, and water hyacinth plants. Charcoal fines obtained from the metallurgical industry were also used. The soils investigated were two Quartzarenic Neosols, QN1 and QN2, from Sergipe State in Northeast Brazil. After mixing with 5% (m/m) of biochar, both soils showed increased water retention capacity, compared to the original samples. The best water retention was achieved using the biochars from palm oil bunch and sugar cane bagasse (absolute increases of 5.5 and 6.5%, respectively) for soil QN1, and the biochars from sugar cane bagasse and water hyacinth plants (absolute increases of 7 and 8%, respectively) for soil QN2. These results could be explained by the polarity of the biochars, as shown by their hydrophilicity, measured by C-13 NMR spectroscopy, as well as by the increased presence of micropores, revealed by SEM analyses, that could physically retain water.