**1. Introduction**

Today, the world is experiencing water stress and it is estimated that by 2030, the demand for water will increase by 50% [1]. This vital liquid must supply more than 7,900 million people around the world [2], a population that continues to increase as well as its economic activity. Added to this, the growing contamination of surface waters, stresses the water available for human consumption, among others. That is why there is an urgent need to develop new technological options for the purification and supply of water. Water containing sulfur, could prove to be an additional source of water for human use and consumption. However, it is known that sulfur can occur in different forms in nature, mainly sulfate and hydrogen sulfide. Sulfur speciation in the liquid medium can be visualized as a function of pH and its exposure to oxygen.

Higher concentrations of sulfate will be found where higher oxygen concentrations are present, mainly surface waters, while hydrogen sulfide will be important in ground water where oxygen is usually depleted. In addition, the water pH will depend on the geographical area and the presence of other chemical or microbial forms in the reservoir or water source [3].

Sulfur, particularly in sulfate form, is abundant in natural effluents, in groundwater where the soil is rich in gypsum, as well as in wastewater from industrial sources [4]. Sulfur-containing water effluents exist throughout the world. However, these waters are normally only used for recreational uses or are discarded, and not considered for human consumption because of their bad smell and taste [4]. However, these waters do not represent a significant risk to human health. An example is the city of Puebla Capital in Mexico, where sulfur-containing water could contribute an additional 7.4% in the supply of drinking water, which is urgently needed, since there are communities that do not receive continuous water service due to limited volumes of water available [5].

Sulfate is not carcinogenic, and its side reactions are limited to stomach problems at concentrations above 300 mg of sulfate per liter in children and above 500 mg L−1 in adults [4]. The World Health Organization (WHO) and the Environmental Protection Agency (EPA), in the United States specify a limit of 250 mg L−1 [6, 7]. In Mexico, sulfate concentration limits are regulated by SEMARNAT (Ministry of the Environment and Natural Resources), with a limit of 400 mg L−1 [8]. These agencies suggest nanofiltration and ion exchange as recommended methodologies for the treatment of sulfates present in water; however, there exist other alternative technologies and materials that could remove sulfate present in water and be used in different countries.

In this review, are describe the existing technologies for sulfate removal, and the information contained in each report will be evaluated. The analysis will be done considering the following factors: availability, economy, speed, and efficiency. Due to the scarce information in the literature on the research topic, no filter is used for the year of publication, everything studied so far had to be considered to maintain a broad and sustained panorama. Finally, are identified and proposed different opportunity areas for sulfate removal.
