Inter-basin water transfers are the root of many conflicts, and water scarcity accentuates them. Those conflicts involve the priority of water use between regions. The Jaguaribe Metropolitan system, located in the Brazilian semiarid region, presents conflicts amongst different water users: irrigated perimeters, industry, and households. This paper analyzed the Jaguaribe Metropolitan water transfer during the 2012–2018 drought by considering environmental and societal aspects. Changes in consumption and users’ drought perception were assessed. The results showed that the drought was longer and more severe in the region that provided water (i.e., Jaguaribe) than in the region that received it (i.e., FMR). Jaguaribe irrigators were aware of the beginning of the drought, but it did not result in immediate consumption control. On the other hand, drought perception was delayed in the FMR. The results of this study suggested that the water allocation decision-making process should include not only the water demands but also the characteristics of the drought and how people perceive it. The main strategy for improving water governance seems to be promoting integrated regional planning and the empowerment of participatory management.

Microcystis sp. is one of the most studied genus of cyanobacteria worldwide. Once it has been identified in raw water, frequent analyses of cell density and toxic metabolites (microcystins) are recommended at the water treatment plants. However, both analytical procedures are highly time-consuming and labor-intensive, allowing the potentially contaminated finished water to reach customers. The identification of easily measurable parameters related to toxin production, preferably by on-line equipment, would mitigate this issue and help water companies to improve water safety and decrease operating costs. However, these devices still have precision limitations and need efficient mathematical models for converting light signals into cyanobacteria densities or cyanotoxin concentrations. In this scenario, this research aimed to develop a mathematical correlation between microcystin production and cell age and density, chlorophyll-a, pheophytin and phycocyanin in a Microcystis aeruginosa culture using a multiple linear regression model. Despite the significant correlation (p < 0.05) found between all the variables and total microcystin, a simplified and precise model (Adjusted R2 = 0.824) involving only phycocyanin and pheophytin concentrations was developed in order to provide an initial attempt to easily and cheaply predict microcystin concentration in raw water.

The evaluation of water quality improvement brought about by in situ treatment of eutrophic water bodies, especially those used for human supply is a challenging task since each water system responds differently. To overcome this challenge, we applied exploratory factor analysis (EFA) to understand the effects of using hydrogen peroxide (H₂O₂) on eutrophic water used as a drinking water supply. This analysis was used to identify the main factors that described the water treatability after exposing blue-green algae (cyanobacteria) contaminated raw water to H₂O₂ at both 5 and 10 mg L^-1. Cyanobacterial chlorophyll-a was undetectable following the application of both concentrations of H₂O₂ after four days, while not causing relevant changes to green algae and diatoms chlorophyll-a concentrations. EFA demonstrated that the main factors affected by both H₂O₂ concentrations were turbidity, pH, and cyanobacterial chlorophyll-a concentration, which are important variables for a drinking water treatment plant. The H₂O₂ caused significant improvement in water treatability by decreasing those three variables. Finally, the use of EFA was demonstrated to be a promising tool in identifying which limnological variables are most relevant concerning the efficacy of water treatment, which in turn can make water quality monitoring more efficient and less costly.