The problems of heavy metals in irrigation water are related to the management-control of heavy metals risk of farmlands and the safe production of crops. There are various sources of irrigation water in the suburb farmlands of Xijiang River. We investigated the sources and distribution characteristics of heavy metals in the irrigation water sources in the riverside and inside-dyke farmlands of Xijiang River. According to correlation analysis, distribution characteristics analysis, single/comprehensive water-quality evaluations of eight heavy metal elements in different irrigation water sources, it was found that nearly 100% of heavy metals were detected in the irrigation water sources in this study. The box plot showed that the average level of cadmium was 0.02 μg·L−1 in this area, and the contents of other elements were mostly in the range of several to dozens of μg·L−1. Most heavy metals were in relatively low concentration level in the irrigation water sources, mercury content level (Quantitative Evaluation Index) was far greater than other elements, followed by arsenic. Arsenic and mercury problems have become more significant problems in local irrigation water sources. Surface water was more likely to be affected by river water and agricultural activities, while groundwater was more likely to be affected by natural causes. The comprehensive water quality evaluation ranged from level I to level III, but the single factor index evaluations of mercury in most water samples and arsenic in two groundwater samples were ‘Inferior’ level. It was suggested that the monitoring of mercury and arsenic (groundwater) in the irrigation water should be strengthened immediately in this area, the disposal measures of farmland water inflow and drainage should be increased if necessary, and reducing the influence of human factors on the natural weathering and leaching of heavy metals is an effective risk avoidance measure in agricultural production in high background regions.