**1. Introduction**

Gastrointestinal diseases have caused up to 871,000 deaths worldwide, which have been related to unsafe drinking water, health, and hygiene. Mortality rate is greater in African countries where death risk is 4.3 × 10−1 [1, 2]. Such data justify that the main risk factors are unsafe water and deficient cleaning linked to malnutrition and immunosuppression, invariable characteristics in marginalized communities. The microscopic parasite *Giardia* is among the main pathogens that cause gastrointestinal diseases at world level. In developing countries, 200 million people have been diagnosed with giardiasis symptoms, which are related to inadequate sanitation problems and access to safe drinking water. Giardiasis does not make a distinction between humans and animals by fecal-oral transmission using different routes: zoonotic, anthropogenic environmental, food, and water [3–5].

The strategy used in this research was assessed by analyzing different literature studies related to *Giardia* risk assessment; the search was performed in databases from October 2000 to October 2016, using the following terms: giardiasis risk factors; *Giardia* cysts in water, air, soil, and food; quantitative microbial risk assessment (QMRA); and cyst treatments. No restriction was found in language. This chapter focuses on reviewing world incidence of *Giardia* in water, soil, air, and food, including giardiasis prevalence, risk factors, and finally a system to reduce cysts in the environment, emphasizing on QMRA.
