Water is an important resource for life and as such, its monitoring is essential. The aim of this study therefore was to estimate concentrations of chlorophyll-a and total suspended solids (TSS) using orbital remote sensing data. The study area was the General Sampaio reservoir, located in the Curu River Basin, in the state of Ceará. The concentration of chlorophyll-a and sediments were mapped based on orbital images captured by the Operational Land Imager (OLI) sensor. The images were acquired on 14 September 2017 and 13 June 2018. The chlorophyll-a concentration was estimated using a model employing a ratio of the blue (450-510 nm) and green (530-590 nm) bands, and the TSS concentration was estimated from the red band (640-690 nm) of the OLI sensor. The chlorophyll-a concentration in September 2017 varied from 37.03 to 43.0 mg L-1, and in June 2018 it ranged from 42.9 to 62.2 mg L-1. The TSS concentration in September 2017 varied from 1.8 to 4.2 mg L-1, while in June 2018, a period that corresponded to the highest local rainfall, the variation was greater, between 2.1 and 17.73 mg L-1. The highest concentrations of suspended sediments were seen in the tributaries of the Curu River and the Salvação Stream. It was possible to estimate the concentrations of chlorophyll-a and TSS using orbital images. The reservoir water was classified as eutrophic throughout the study period.

The increase in irrigated areas and the water crisis in numerous regions have encouraged the use of irrigation systems and management that afford greater efficiency in the use of water. Wastewater is one option for maximising this efficiency. The aim of this study was to evaluate the indicators of water productivity in the cultivation of irrigated cowpea under different production systems. The study was carried out in the experimental area of the Sewage Treatment Station (ETE) located in Tianguá, Ceará. The experiment consisted of six production systems (treatments) in subdivided plots distributed in a completely randomised design (CRD) with fifteen replications in a (2 x 3) factorial scheme, i.e. two sources of water and energy: drinking water + electricity from the electrical grid (conventional system) and wastewater + solar photovoltaic energy (alternative system), and the different sources of fertiliser (mineral and organic), in addition to the control treatments. The water productivity indicator that expresses the relationship between the yield of the crop and the volume of water applied was determined, and the index in economic terms between crop yield and the volume of water applied. The system using wastewater and organic fertiliser showed better water productivity, 0.422 kg m-3, while the system that used drinking water with no fertiliser showed less efficiency, 0.188 kg m-3. Water use efficiency in the systems that used wastewater was higher in relation to the systems that used drinking water. Irrigation with treated domestic effluent increases water productivity and water use efficiency, in addition to being a strategy for agricultural exploitation under conditions of water scarcity