38 Drinking Water

Radiological substances can be present in drinking water; they are categorized as either human made or naturally occurring. Generally, they are found in low concentrations and may not pose a significant threat to human health. Human-made radioactive substances are often controllable when they enter the water, while naturally occurring substances can enter at any point and are harder to control. Naturally occurring substances typically result in higher radiation levels compared to human-made ones (Kekes et al., 2023). (AMM)

Physical pollution of water involves naturally occurring contaminants in sources of water such as organic materials that fall into the water like leaves, sediments, and heat. These pollutants can degrade water quality by altering the color and odor (Kekes et al., 2023). (AMM)

Health Impacts of Contaminated Water 

Water is a basic human right, but not everyone has as easy access to drinking water as they should. Water scarcity refers to how much water is available in an area compared to how much people use it. It is a measurable fact that shows if there is enough water in a specific area or not. Water stress refers to the ability to look at whether people and nature can get the water they need. Not only does it include water availability, but also water quality, how easy it is to access, and how accessible it is for environmental needs. Water risk refers to the chance of facing problems related to water, such as water shortages, pollution, or bad infrastructure. Different groups and industries experience water risks in different ways (Schulte, 2021). According to the World Health Organization, in 2021, over two billion people throughout the world lived in water-stressed regions. This situation is unfortunately worsening due to a combination of climate change and population growth. (AMM)

According to the same WHO article, in 2022, there were six billion people who had access to safely managed drinking water services. These services included improved water sources located on premises, available when needed, and free from contamination. However, the remaining two billion people still lacked safely managed services. Among them, 1.5 billion people had basic services, which meant an improved water source within a thirty-minute round trip. Additionally, 292 million people have limited services, which required more than thirty minutes to collect water. 296 million people relied on unprotected wells and springs. While the remaining 115 million people collected untreated surface water from lakes, ponds, rivers, and streams (Drinking Water, 2023). (AMM)

The economic and social impact of access to water is something many people take for granted. Improved water access reduces time spent collecting water, therefore improving productivity and safety. Access to these better water sources also means less money being spent on health since people are less likely to become sick. This can lead to an increase in school attendance and even improve long-term well-being for an increase in livelihood. Improved water infrastructure supports economic growth, job creation, and sustainable agriculture. WHO sets global water safety guidelines and helps countries develop health based water regulations. They do this to ensure universal access to clean water because it is critical for good health, economic stability, and sustainable development worldwide. (AMM)

Drinking water treatment methods are classified into two main categories: physical methods and chemical methods. Water purification can be achieved using either a single method or a combination of methods, depending on regulatory standards and the characteristics of the raw water. The most commonly used methods are evaluated based on their efficiency, necessity, and applicability (Kekes et al., 2023). Table 1 identifies some of the most commonly used methods depending on their nature. (AMM)

Table 1: Most commonly used drinking water methods (Source: MDPI)

Method	Nature of Method
Screening	Physical
Coagulation-Flocculation	Chemical
Dissolved Air Flotation (DAF)	Physical
Clarification	Physical
Filtration	Physical
Membrane Filtration	Physical
Adsorption	Physical or chemical
Ion exchange (IX)	Chemical
Advanced Oxidation Processes (AOPs)	Chemical
Disinfection	Physical or chemical

Screening is a preliminary water treatment method used to remove large solids and grits from water to prevent damage to treatment equipment. There are two types of screens, coarse screens for large solids and fine screens for smaller materials. Screens can be cleaned either mechanically, which often reduces labor costs and improves efficiency, or manually, which is more suitable for small-scale plants but requires frequent maintenance (Kekes et al., 2023). (AMM)

Coagulation-Flocculation is a conventional method for treating drinking water with visible cloudiness. This method is effective when dealing with the presence of particles in the water so the water will be more appealing to consumers. Coagulation involves adding chemical agents, such as aluminum sulfate or iron salts, to neutralize small, negative charged particles. Once the particles are neutralized, they become unstable and start to collide, forming small agglomerates known as flocs. As these collisions continue, larger agglomerates form, which is a process known as flocculation. These larger flocs can then be removed by physical processes like clarification. This combined method effectively removes suspended particles and dissolved contaminants, improving the water’s appearance and taste (Kekes et al., 2023). (AMM)

Dissolved Air Flotation (DAF) is an alternative method to the conventional clarification process. It is used after the coagulation-flocculation process, especially for water with high oil concentrations, grease, and suspended particles. DAF introduces air bubbles at the bottom of the tank, which rise and collide with particles, forming agglomerates that ascend to the top and form a sludge blanket. The sludge is then mechanically removed. This process is displayed in Figure 2. DAF is cost-effective and efficient, particularly with small bubbles and the use of chemical flocculants (Kekes et al., 2023). (AMM)

Clarification is another conventional physical water treatment method that typically follows coagulation-flocculation and precedes filtration. The main purpose of clarification is to remove suspended particles like silt, algae, mud, and agglomerates from raw water. This process usually involves sedimentation, where water is slowed down in large, open tanks to allow particles to settle out under the influence of gravity. The settled particles form sludge, which is then removed for further treatment and disposal (Kekes et al., 2023). (AMM)

Filtration is also a conventional physical water treatment that follows clarification. It involves passing water through a medium or membrane to separate suspended particles. The filter medium, which can be made up of materials like sand, crushed anthracite, or garnet, retains particles while allowing clean water to pass through. This process effectively reduces water turbidity and provides protection against cysts and pathogens. The efficiency of filtration depends on the medium porosity, permeability, tortuosity, and connectivity (Kekes et al., 2023). (AMM)

Membrane filtration is a subcategory of the conventional filtration process. It uses porous membranes as perm-selective barriers to separate pollutants from water. This process results in purified water on one side of the membrane and a concentrated solution containing the pollutants on the feed side of the membrane (Kekes et al., 2023). (AMM)

Adsorption is a water treatment process that can serve as an alternative to chemical coagulation and clarification. It involves three main elements;

• Liquid phase: polluted water.
• Adsorbates: pollutants that need to be removed.
• Adsorbents: materials that attract and hold the pollutants, usually carbon.
  

  

The main goal of adsorption is to transfer the pollutants from the water onto the absorbent. Adsorption can either be physical, using can der Waals forces, or chemical, forming bonds through electron rearrangement. The process continues until adsorption and desorption rates are equal, meaning no further pollutants are collected (Kekes et al., 2023). This process is shown in Figure 3. (AMM)

Ion exchange (IX) is a newer water treatment method that is often used to enhance other processes like coagulation by removing natural organic matter (NOM) and softening water by eliminating calcium and magnesium. It uses resins for positive and negative ion exchange. The process continues until all ions on the resin are exchanged. This method is effective for removing specific contaminants based on their properties and the type of resin used (Kekes et al., 2023). (AMM)

Advances oxidation processes (AOPs) are water purification methods that break down harmful organic and inorganic pollutants, including pharmaceuticals and substances that cause bad taste or odor. AOPs work by producing hydroxyl radicals (*OH), which is a highly reactive molecule that can destroy most contaminants through two main chemical reactions. These reactions ultimately turn pollutants into harmless byproducts like carbon dioxide and water. AOPs can either be photochemical or non-photochemical (Kekes et al., 2023). (AMM)

Disinfection is an important water treatment process that aims to eliminate hazardous microorganisms, such as bacteria, viruses, and protozoa. Disinfection also targets harmful organic and inorganic compounds to ensure safe water for consumers. Methods can be chemical, such as chlorine or iodine, or physical, like heat or UV light. The effectiveness of these methods mainly depends on the disinfectant dose and the contact time between the agent and the water (Kekes et al., 2023). (AMM)

These physical and chemical treatment methods form a multi-barrier approach to ensure drinking water is safe, drinkable, and compliant with regulatory standards. Each methods plays a distinct yet complementary role. Together, their combined application is essential for addressing a wide range of contaminants found in water sources. (AMM)