Nano-silica addition improves mechanical and durability behavior in mortars. However, nanomaterial 46 handling requires use of occupational risk prevention measures as Individual Protection Equipment for 47 the workers. Moreover, the high agglomeration of nanomaterials produces uncertainty in the expected 48 mortar performance. Rice husk ash as a source of reactive silica in cement compositions is compared with 49 nano-silica. The use of rice husk ash provides similar physical-chemical cementitious materials than 50 other commercial nano-silica providing relevant differences during the composition. Near 50% wt of 51 volatility is found for the silica nanoparticles during the handling dosage. Thus, the rice husk ash presents 52 a reduced volatility, $12% wt and it allows ensuring high content with adequate workability. Mortars 53 with addition of rice husk ash reach higher compressive strength and resistivity in correlation with lower 54 porosity. For that, the use of rice husk ash is viable as safer alternative material than nano-silica in the 55 cementitious compositions. In addition, as the rice husk ash comes from agricultural waste resources 56 their use as secondary raw material will contributes to circularity in the economy by reducing engineered 57 nanomaterials consumption. 58

This chapter analyses the urban water cycle in the smarts cities, describes the current situation, which constitutes a valid but outdated knowledge, adopting the perspective of improving and extending the measures that lead to greater efficiency of the water collection, treatment, supply, sewage, purification, and reuse systems at all stages of the water cycle: the sites, construction, operation, and maintenance of the networks and systems that enable the cycle to be completed effectively. The process of converting a city into smart city includes resources, processes, and services, and all stages of the water cycle are a set of processes, with water as a fundamental resource, which condition the different services to citizens, and therefore, it is necessary to try to establish efficiency improvements in all of them.