Importance of water and the natural water cycle
Water is an absolutely irreplaceable resource that sustains life on Earth. The human body consists of 63–65% water, which serves as a universal solvent and participates in thermoregulation and metabolism.
The daily physiological requirement is 1.5–2 L, but during heavy labor or in hot weather, it increases to 10–12 L. Domestic consumption standards depend on plumbing infrastructure: in cities, this is about 326 L/day per person.
The unity of all waters in the hydrosphere is maintained by the water cycle, driven by solar energy and gravity. The small (short) cycle returns precipitation directly to the ocean, while the large (long) cycle transports moisture to the continents. Water has a high heat capacity, performing a crucial climatic function.
Sources and structure of hydrosphere pollution
Although there is enough fresh water on the planet, its massive pollution creates the threat of a water crisis. The World Ocean has become a global collector of waste.
Key pollution sources:
- Industrial wastewater (led by the woodworking, chemical industries, and electric power generation).
- Household wastewater and drainage water.
- Runoff from populated areas and livestock complexes.
- Water transport and oil production.
Priority pollutant: oil. It forms a film that blocks gas exchange, leading to the death of plankton and marine animals. A secondary consequence of oil pollution is the pathological proliferation of toxic golden algae, capable of destroying all life over vast areas.
Epidemiological hazard
Water can serve as a transmission route for numerous diseases. When untreated sewage enters water bodies, large-scale waterborne epidemics occur.
Waterborne diseases:
- Intestinal infections: cholera, typhoid fever, dysentery.
- Viral infections: hepatitis A, poliomyelitis.
- Zoonotic and parasitic diseases: leptospirosis, tularemia, giardiasis.
- Contact transmission (during swimming): scabies, fungal infections.
Characteristic features of waterborne epidemics: suddenness, mass scale, connection to a common source, mild clinical course, absence of morbidity among infants, and the presence of a "contact tail" after the outbreak is eliminated.
Chemical pollution and non-infectious pathologies
The chemical composition of drinking water directly affects health. Deviations from the norm lead to non-infectious diseases:
- Hardness (calcium and magnesium): high hardness worsens the domestic properties of water and provokes the development of urolithiasis.
- Fluoride: deficiency (less than 0.5 mg/L) causes dental caries.
- Nitrates and nitrites: cause toxic cyanosis (methemoglobinemia), which is especially dangerous for infants on formula feeding (the maximum allowable concentration [MAC] of nitrates in the Russian Federation is 45 mg/L). Additionally, they can transform into carcinogenic nitrosamines.
The presence of nitrogen salts in water (ammonium, nitrites, nitrates) serves as an indirect indicator of organic fecal contamination. Ammonium salts indicate fresh contamination, nitrates indicate old contamination, and their triad indicates continuous sewage discharge.
Briefly: answers to topical questions
What are the standards and maximum allowable concentrations (MAC) of harmful substances in drinking water according to SanPiN?
Drinking water must be safe in epidemiological and radiation terms, harmless in its chemical composition, and have favorable organoleptic properties. The main maximum permissible standards:
| Parameter | Centralized sources | Non-centralized sources |
|---|---|---|
| Odor and taste (points) | 2 | 2–3 |
| Color (degrees) | 20 | 30 |
| Turbidity (mg/L) | 1,5 | 1,5–2,0 |
| Total hardness (mEq/L) | 7–10 | 7–10 |
| Nitrates (mg/L) | 45 | 45 |
| Total mineralization (mg/L) | 1000 | 1000–1500 |
| Sulfates (mg/L) | 500 | 500 |
| Chlorides (mg/L) | 350 | 350 |
| Iron (mg/L) | 0,3 | 0,3 |
The microbiological standard for drinking water based on the total bacterial count is no more than 50 CFU/mL.
What methods of drinking water disinfection are used at water treatment plants?
Reagent and non-reagent methods of water disinfection are used at water treatment plants.
- Chlorination is the most common reagent method. It includes chlorination with normal doses, hyperchlorination, double chlorination, as well as the use of chlorine dioxide and pre-ammoniation.
- Ozonation is a promising reagent method in which ozone destroys pathogens by inactivating bacterial proteins.
- Ultraviolet irradiation is a non-reagent method using bactericidal mercury-quartz or argon-quartz lamps.
- Ultrasound is an alternative non-reagent disinfection method.
The nitrogen triad as a pollution traffic light: Ammonium (fresh) — red light (high hazard); Nitrites — yellow; Nitrates (old) — green (the mineralization process is complete, but it is still not worth drinking).
Class and exam questions
What is the epidemiological significance of water?
Water acts as a vehicle for the transmission of infectious and parasitic diseases (cholera, typhoid fever, hepatitis A) when contaminated with fecal and domestic sewage.
How does oil pollution affect atmospheric oxygen?
The oil film disrupts the gas exchange of water bodies and kills oceanic phytoplankton, which generates about 60% of all oxygen on the planet.
What does the detection of ammonium salts in water indicate?
This indicates fresh organic pollution (the initial stage of protein decomposition) and points to a high epidemiological hazard.
What are the health hazards of excess nitrates in drinking water?
Nitrates are reduced to toxic nitrites, which oxidize hemoglobin to methemoglobin, causing hypoxia (especially in infants), and can also form carcinogenic compounds.
What else to study on this topic
- Detailed structure and links of the small and large water cycles
- Classification of surface and underground water bodies
- Toxicokinetics and pathogenesis of methemoglobinemia
- Differential diagnosis of fecal and geological water contamination
- Domestic water consumption standards depending on infrastructure and amenities
Master the entire topic in the "Hygiene" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Ecological and Hygienic Problems of the Hydrosphere" plus 530 more pages on the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 95 video lessons for the subject
Other topics in "Chapter 2. Ecological and Hygienic Problems of the Hydrosphere and Water Supply"
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