## 4 Discussion  
The use of AWGs as a solution to water scarcity has the advantages of simplicity of implementation and energy-free or renewable-energy operation. However, at the same time, there are also disadvantages in terms of seasonality, geographical location and climates [40]. The climatological study developed shows that the conditions of the Matehuala, SLP, region are favourable for the design and use of AWGs for the harvesting of atmospheric air water. The literature notes that favourable conditions for AWG use are above 40% RH (\(\geq\) 40%) [42]. With an average annual humidity of approximately 60% despite being a semi-arid region, the humidity levels are suitable for the application proposed in this work. To evaluate the profitability and functionality of the AWG, a new moisture harvest index (MHI) presented in [52] was introduced, which relates the latent heat of condensation to the total heat transfer in the dehumidifier. This index establishes that the economic, energy and operational conditions are unfavourable for the use of AWGs in conditions or regions that have an MHI \(<\) 0.3. For the region studied from the psychometric chart, the values of the MHI can vary in the proposed range of temperatures and humidity of approximately 0.3 to 0.45, the former being the worst case and the latter the best case that can prevail in the region. However, air quality is one of the parameters that is most questioned in the use of AWGs because it is related to the quality of the water collected. There is little literature devoted to the study of inhalation as a route of exposure to arsenic, whereas most consider that the main exposure is based on oral exposure through drinking water or as indicated by CSTEE (2001), through food. However, CSTEE (2001) states that, although air is not a major route of exposure in quantitative terms, the presence of arsenic in the environment is due to the following: Air \(<\) 1%, cigarette smoke 0-16%, fresh water 0-33% and food 50-98% [53]. Human exposure to arsenic through air generally occurs at very low concentrations ranging from 0.4 to 30 ng/m\({}^{3}\). The United States Environmental Protection Agency has estimated that approximately 40 to 90 ng of arsenic per day are inhaled by humans. In non-contaminated areas, approximately 50 ng or less of arsenic per day are inhaled [54; 55]. A very recurrent discussion in scientific forums is whether arsenic or contaminants in the air affect the quality of water collected by the AWG or by collecting rainwater. There are no exact data on arsenic levels in the air in the study region, but results found in scientific review show that the levels should be acceptable, without greatly affecting the quality of water harvested from the atmospheric air. It has been reported that the water harvested from the atmospheric air [56; 57; 58] presents important quantities of faecal, while parameters such as pH, hardness, dissolved solids,  
Figure 10: Cost per litre of water produced by the atmospheric water generator. and conductivity, heavy metals, alkalinity, odour, flavour, nitrites and nitrates are within the limits established by national standards for drinking water. Few studies report the presence of arsenic in harvested water; the arsenic indexes reported are less than 0.007 mg/L, thus remaining within the standard of water for human consumption [59]. In Mexico, rainwater has been harvested [27] in which very low levels of fluoride and arsenic have been measured in the water collected. A maximum concentration of 0.004 mg/L was found, well below NOM-127-SSA1-1994 [60] (0.025 mg/L) and WHO guidelines [61] (0.010 mg/L). The water harvesting procedure does not contemplate water coming into contact with soil. In contrast in [47] they report arsenic levels of 0.2 mg/L in the water collected from rain that entered into contact with soil. In general, it is reported that water captured from the environment has excellent conditions for human use as long as it goes through a process of microbiological quality improvement [62].