Freshwater is a critical component for social and economic sustainability, but also the water scarcity is a foremost threat nowadays.During the last century, many governments have been implementing public policies for reducing the water consumption, optimize the potabilization processes, and promote cleaner techniques for wastewater treatment such as desalinization, heterogeneous photocatalysis, oxidation processes, ozonation, and so on.The review begins with a short presentation of the first explored water purification techniques starting from the Bronze Age, then, it is presented the minimum quality parameters and comments that disinfection, decontamination, and desalinization of wastewater and seawater must achieve.It is also reviewed several water purification methods based on microbiological, chemical and physical techniques.This review conveys a fine reviewing of solar stills, solar collectors and heterogeneous photocatalysis, presenting characteristics and latest innovations from several researchers.Finally, the residual products from those techniques are also called "by-products", therefore, it is explained the main methodologies that current researchers are employing for reducing, but also for exploitation of by-products in two or three-stage (fish farming or crop irrigation) processes.