# Photocatalytic Inactivation as a Method of Elimination of _E. coli_ from Drinking Water
## 1 Introduction  
Water is an essential natural resource and, perhaps, the greatest need of humanity for health, wellbeing, development, and sustenance of life [1, 2, 3]. Its availability and accessibility plays an important role in food production, poverty reduction, social welfare and economic development [1]. Water has so many functions in the body, such as the maintenance of the normal volume and consistency of blood and lymph, modulation of moisture content of internal organs of the body, removal of poisons or toxins from the body through urine, sweat and breathing, the regulation of body temperature. It is also essential for the regulation of the normal structure and functions of the skin [1]. Unfortunately, about 20% of the world's population has no access to clean drinking water, a problem which is further complicated by the increasing world population [4]. According to the World Health Organization report of 2015, more than 2.6 billion people lack safe drinking water, leading to the death of about 3.4 million people from various water related diseases each year. Of these deaths, 1.4 million were reported to be children [5, 6]. The exposure to preventable health risks has been attributed to the absence, inadequacy, or inappropriately managed water and sanitation services. Some of the health risksand diseases associated with the lack or insufficient clean water supply include hepatitis, cholera, typhus, polio, tuberculosis, diphtheria and diarrhea. These have become a problem of global concern [7,8]. Diarrhea is largely preventable, but it remains the most widely known disease linked to contaminated food and water. About 829,000 yearly deaths are attributed to diarrhea, and this is due to unsafe drinking-water, poor sanitation, and inadequate hand hygiene [7]. Although these water-related diseases are common in developing countries, they are also a challenging health concern in the developed world [3,6]. Thus, water quality control from water treatment plants continues to be an important global topic of public health concern in the water industry. Shortage of fresh and portable water supply is also combated through water recycling and reuse. However, this is also constrained due to the need to completely eliminate contaminants in waste water [9]. Hence, the decontamination of water from both chemical and microbial (biological) contaminants is a major problem that must be solved especially in developing nations of the world. Microbial contaminants are often considered a higher priority than chemical contaminants because the adverse health effects of microbial contaminants are immediate, while that of chemical contaminants are connected with long-term exposures [2]. Most biological agents that cause water borne diseases are transmitted to humans via sewage discharge into water sources [8]. In water treatment plants, a simple and reliable microbiological water quality control of drinking water is often required to assess and monitor the presence of these pathogens, especially the faecal coliforms [1,6]. These are a group of bacteria that emanate from the faecal droppings of livestock, wildlife and humans. _Escherichia coli_ (_E. coli_) is the most abundant of this category, and it is often associated with the health risk of water [3,6]. There is a high possibility of the presence of other harmful viruses and bacteria of faecal origin when _E. coli_ is present in water samples. Pathogenic microbes such as Giardia, Cryptosporidium, and Shigella may also be found in water samples where _E. coli_ is present [3]. This is why _E. coli_ is often used as an indicator organism or a benchmark for determining water purity and for the assessment of water samples containing fecal contaminants beyond acceptable levels [1,3,6,8]. Two key factors are responsible for the use of _E. coli_ as the preferred indicator for the detection of faecal contamination in drinking water: firstly, some faecal coliforms are non faecal in origin; and, secondly, there are well-developed and improved testing methods for _E. coli_[1].