Understanding Water Types and Characteristics
General Characteristics of Different Water Types
Freshwater
Freshwater has a low concentration of dissolved salts, making it tasteless. It’s primarily found on land, in ice, and in the atmosphere. However, there are various types of freshwater based on their unique characteristics.
Hard Water and Soft Water
Freshwater can be categorized into hard water and soft water depending on the dissolved salts and ions. Hard water contains high levels of positive ions, mainly calcium and magnesium. These ions can deposit in narrow tubes, causing calcification. They also hinder the dissolution of substances like sugar, salt, or soap, making washing more difficult. Hard water is common in regions with limestone and dry climates. Soft water, on the other hand, lacks these ions, making it easier to dissolve other substances.
Distilled Water
All-natural waters contain some dissolved ions and salts. Distilled water is created by removing almost all ions and salts through boiling and condensing the water vapor in a controlled environment.
Raw Water
Raw water is untreated water collected directly from its source. It may or may not be suitable for human consumption.
Drinking Water
Drinking water is safe for human and animal consumption. It’s a type of freshwater that can be either hard or soft. Health authorities ensure its safety by analyzing and treating raw water to meet potability standards.
Gray Water and Wastewater
Used water returns to nature with varying levels of contamination. Gray water is moderately polluted water from household use, containing detergents, human waste, grease, dust, and mud. When gray water from a community mixes, it becomes sewage, which is significantly more contaminated. When black and gray water are channeled through a sewer system, it’s called wastewater. Wastewater requires treatment to remove contaminants before being returned to the environment. Untreated wastewater can be a potent pollutant, disrupting natural cycles.
Surface Water and Groundwater
In nature, water flows on the surface (surface water) and infiltrates the soil (groundwater). When groundwater accumulates underground without drainage, it forms standing water. Dead water is standing water with high nutrient levels and oxygen depletion, supporting only anaerobic life.
Springs and Hot Springs
Groundwater eventually emerges at specific points called springs, creating spring water. If the water’s path encounters areas near the Earth’s mantle or volcanic intrusions, it heats up and surfaces as hot springs, often used for medicinal purposes. Medicinal waters are those with health benefits.
Aquifers and Fossil Water
Some infiltrated water is stored in underground reservoirs called aquifers. Fossil water is found in aquifers that have been sealed for centuries or even millennia.
Magmatic and Metamorphic Water
Volcanic rocks and rocks under high pressure contain water that is released during state changes. These are magmatic water and metamorphic water, respectively, but they are scarce on Earth.
Classification According to Use and Origin
Classification of Water by Source
- Surface water (river water)
- Well water
- Lake and pond water
- Seawater
- Rainwater
- Distilled water
- Purified water
Each type of water contains dissolved, suspended, or colloidal minerals and gases in varying amounts depending on its source.
Classification of Water by Use
- Domestic water (cleaning and washing)
- Industrial water
- Steam generators (high and low pressure)
- Cooling water
- Water for chemical analysis
- Water for biological applications (pyrogen-free)
Water Treatment Methods
Screening
Screening is a mechanical separation technique that uses a mesh or sieve to separate solids of different sizes.
Aeration
Aeration involves vigorously shaking a container of water or allowing water to drip through perforated trays. This removes volatile substances like hydrogen sulfide, which affect odor and taste, and oxidizes iron and manganese, forming precipitates that can be removed by settling or filtration.
Storage and Sedimentation
Storing water in clean conditions for a day can eliminate over 50% of bacteria. Longer storage leads to further reductions. During storage, suspended solids and some pathogens settle to the bottom. Water drawn from the top will be clearer and contain fewer pathogens.
Disinfection by Boiling
Boiling water vigorously for 10-12 minutes disinfects it. Most pathogens, including cholera, are destroyed at 100°C within a minute, and many die at 70°C. The main drawbacks of boiling are fuel consumption and time.
Chemical Disinfection
Chlorination is the most common method for disinfecting water. The chlorine source can vary.
Filtration
Filtration includes mechanical screening, absorption, and biochemical processes, especially in slow sand filters. Depending on the filter’s size, type, depth, flow rate, and the raw water’s characteristics, filters can remove suspended solids, pathogens, certain chemicals, tastes, and smells.
Coagulation and Flocculation
If water contains suspended solids, coagulation and flocculation can remove much of it. In coagulation, a substance is added to alter the behavior of suspended particles. Flocculation, a gentle agitation process following coagulation, allows particles to collide and form larger particles that can be separated by settling or filtration.
Desalination
Excessive salts can give water a bad taste. Desalination by distillation removes salts and can be done using various methods, even at the household level, for example, to treat seawater. Desalination also removes other chemicals like fluoride, arsenic, and iron.
Inorganic and Organic Constituents
Inorganic Constituents
Inorganic constituents come from contact with the environment: the atmosphere (gases), soil (minerals), and human-contaminated environments. Rain dissolves atmospheric gases like nitrogen, oxygen, carbon dioxide, and sulfur dioxide. Major constituents stabilize natural water chemistry. The pH of natural waters ranges from 7 to 9, while the pH of oceans is 8-8.4. Toxic heavy metals are present in very low concentrations. Consequently, most natural waters mainly contain calcium, magnesium, and sodium cations, and bicarbonate, sulfate, and chloride anions. Besides natural levels, industrial, agricultural, and domestic activities can introduce high concentrations of specific inorganic ions.
Organic Constituents
Organic constituents come from runoff that has contacted decaying vegetation, animal excrement, or aquatic life waste. Human activities also contribute organic elements through runoff or direct discharges.
Physical and Chemical Parameters
Physical Parameters
Physical parameters include turbidity, color, smell, taste, conductivity, and resistivity.
Chemical Parameters
- Alkalinity
- Colloids
- Mineral acidity
- Solids
- Chlorides
- Sulfates
- Nitrates
- Fluorides
- Bicarbonates and carbonates
- Toxic metals (arsenic, cadmium, lead, chromium, barium, and selenium, which require strict control and are measured by atomic absorption spectrophotometry)
Ash Analysis
Ash analysis determines the inorganic residue left after burning or completely oxidizing organic matter in food. Understanding the characteristics of different ash analysis methods and the necessary equipment is crucial for reliable results. There are three types: dry ashing (for most food samples), wet ashing (for high-fat samples like meat), and low-temperature plasma dry ashing (for volatile element analysis). This lab session will use dry ashing, which involves burning the sample in a muffle furnace to remove all organic material. The remaining ash is the inorganic residue. Total ash measurement is useful for determining various minerals in food. Potential errors in dry ashing include ash loss due to flame intensity, mineral changes during heating (e.g., carbonates to oxides), sample adhesion with high sugar content, and fusion of trapped non-oxidized carbon.
Moisture Content
Moisture content is crucial for preserving certain products, affecting the stability of dehydrated fruits and vegetables, dried milk, powdered eggs, dehydrated potatoes, and spices. Moisture determination is a quality factor for jellies and jams (to prevent sugar crystallization), sugar syrups, and prepared cereals. Moisture reduction is used for convenient packaging and shipping of milk powder, sweeteners, and dehydrated products (which are difficult to pack with high moisture content). Moisture content is often specified in standards of identity, e.g., cheddar cheese must have <39% moisture, and flour must have <15% moisture. All nutritional value calculations require knowing the moisture content. Moisture content data are used to express other analytical results consistently (e.g., on a dry weight basis).
pH Control in Food
Controlling pH in food is important to avoid problems or illnesses. Excessively acidic food can harm the stomach, causing diarrhea. Some acids can damage proteins, which are essential for the body.
Potentiometer and pH Meter
A solution’s pH can be measured by titration, which involves neutralizing an acid (or base) with a known concentration of base (or acid) using an indicator (a compound that changes color with pH). It can also be determined by measuring the electrical potential generated by special electrodes immersed in the solution.
Potentiometer
Potentiometers measure electrical quantities like current, charge, potential energy, resistance, capacitance, and inductance, usually expressed in standard electrical units.
pH Meter
A pH meter measures a solution’s pH. Designs and sensitivity vary, but essential components include a glass electrode, a reference electrode, and a voltmeter calibrated to read pH units directly. The glass electrode relies on the unique property of a thin glass membrane, which generates a potential difference when its sides are in contact with solutions having different hydrogen ion concentrations. In use, the entire electrode is immersed in the unknown solution, and the membrane contacts two solutions: one with a known pH and the other with the unknown pH. The arrangement ensures that the voltmeter measures the potential difference solely due to the difference in hydrogen ion concentrations.