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Species inhabiting arid environments often contend with ambient temperatures as high as 45 degrees C and that are coupled with unpredictable availability of resources. Free-standing water has been considered to be a resource that limits distribution and abundance of many species of wildlife in arid regions of the United States, and water developments have been used since the 1940s to improve habitat. Provision of water has been assumed to be beneficial to wildlife, particularly during dry seasons and in those environments where surface water is scarce. In recent decades, degradation of naturally occurring water sources resulting from anthropogenic factors has further decreased surface water available to wildlife. Nevertheless, water developments have become controversial, in part, because their ecological effects are difficult to quantify. We compiled and evaluated recently available literature for evidence of effects of water sources on wildlife populations. Critics have expressed concern about water quality, species-specific benefits, mortalities of entrapped animals, enhancement of predator populations, increases in predation rates near water sources, and competition; in general, these negative effects are not supported by available data and remain highly speculative. Positive effects of water developments on wildlife have been documented, and species thought previously not to use free-standing water do so when it is available. Long-term studies with strong experimental designs are needed to examine the effects of water developments on productivity, recruitment, and survival of wildlife populations.