The state of drinking water is one of the main problems of our time. That is why the analysis of the quality of tap water is so important. Pollution of open water bodies is associated with the activities of industrial enterprises, transport, and human economic activities.
Important aspects
It is necessary to have an understanding of the main contaminants of drinking water that adversely affect human he alth. The analysis of tap water in Moscow is carried out on the basis of the laboratory of sanitary and epidemiological control according to approved methods.
According to the results of studies, about 75 percent of the samples pose a threat to human he alth, and a significant excess of the concentration of toxic compounds was found in 12%.
The quality of drinking water is undoubtedly an urgent and serious problem of our time, which is why the chemical analysis of tap water is so important.
Quality Metrics
They are divided into several groups:
- organoleptic, to whichinclude smell, haze, color;
- chemical (various chemical compounds are included);
- microbiological.
The color of water is due to the presence of complex iron compounds, it is measured visually. The smell of water is given by volatile substances that enter it along with sewage. The cause of turbidity is considered to be a variety of finely dispersed substances. The source of the taste of tap water can be organic substances of plant nature.
Classification by chemical composition
In order to analyze tap water, you need to know the main chemical compounds that may be included in it.
Components are divided into six groups according to their chemical composition:
- Basic ions (macroelements), which include cations of potassium, magnesium, calcium. They make up 99.98% by weight of all s alts dissolved in water.
- Dissolved gases (oxygen, hydrogen sulfide, nitrogen, methane).
- Biogenic substances are represented by compounds of phosphorus and nitrogen.
- Trace elements are metal ions that occur in small amounts.
- Dissolved organic substances, which include alcohols of a limiting and unsaturated series, aromatic compounds, hydrocarbons, and nitrogen-containing compounds. When assessing their quantitative content, the permanganate or dichromate oxidizability of water (COD), as well as biochemical oxygen demand is calculated.
- Toxic pollutants - heavy metals,petroleum products, organochlorine compounds, phenols, synthetic substances (surfactants).
Evaluation parameters
Analysis of tap water involves the determination of the following characteristics:
- The content of s alts in it (in terms of calcium bicarbonate).
- Alkalinity of water. It is determined by titrating a water sample with a strong acid, such as hydrochloric acid, in the presence of phenolphthalein (pH of the color transition is 8.3), then methyl orange (pH of the color transition is 4.5).
- Oxidation. For drinking water, it cannot exceed 100 mg/l (permanganate method).
- Water hardness. Hardness is determined by the number of millimol equivalents of calcium and magnesium ions contained in 1 liter of water (mol/l). For drinking purposes, water with medium hardness is used.
Determination of chloride ions by titration of silver nitrate
In this case, the analysis of tap water is carried out according to a special technique. One hundred milliliters of water is taken, then chlorides are determined in it at a concentration of up to 100 mg per 1 liter. To analyze tap water, the sample is introduced into clean conical flasks, then one milliliter of potassium chromate solution is added. One sample is titrated with a solution of silver nitrate until a faint orange tint is detected, the second is used as a control sample. Next comes the processing of the results, comparing them with tabular data.
Water hardness analysis
Let's try to understand how to analyze tap water in order to identify its hardness. According tomethod, 100 ml of filtered tap water are added to a conical flask. Then add 5 ml of a buffer solution, then 5-7 drops of a chromogen-black indicator and titrate with vigorous stirring with a 0.05 N solution of Trilon B until a stable blue color appears. Next comes the processing of the results, comparing them with acceptable standards.
Determination of bacteria using titrimetric analysis
Having figured out where to test tap water, let's try to understand how to determine the presence of bacteria in samples of tap water.
The titration method is suitable in cases where the required equipment and materials are not available to carry out membrane filtration. It is based on the formation of bacteria after sowing a certain volume of water in a nutrient liquid medium, followed by their re-seeding on a special nutrient medium with lactose. Next, the colonies are identified by cultural and biochemical methods.
When examining tap water with a qualitative method (suitable for current sanitary supervision, production control), three sample volumes of one hundred milliliters are inoculated.
Each volume of analyzed water is inoculated into a lactose-peptone medium. Sowing 100 milliliters and 10 ml of tap water is carried out in 10 and 1 ml of concentrated lactose-peptone medium. Next, the crops are placed in an incubator at a temperature of 37 ºС for one or two days. Not earlier than after a day of incubation, a preliminary assessment of the samples is carried out. In containers where turbidity is detected, gas is observed,inoculate with a bacteriological loop on fragments of the Endo medium, while obtaining isolated colonies. Capacities without signs of growth are left in a thermostat and analyzed again after two days. Crops that do not have signs of growth are called negative and are not used for further research.
From the containers in which the formation of gas was detected, turbidity appeared, or there is one of these signs, crops are carried out on the sectors of the Endo medium. Crops on the Endo medium are incubated at 37 ºС for 18-20 hours. When turbidity and gas are detected in the accumulation medium and an increase on the Endo medium of colonies characteristic of lactose-positive bacteria, dark red or red, having a metallic luster (without luster), convex with a red center and an imprint on the nutrient medium, the presence of common coliforms in this volume of the sample is ascertained. bacteria.
The presence of the OKB needs to be additionally confirmed experimentally. If only turbidity was detected in the accumulation medium, then belonging to lactose-positive colonies is a doubtful fact. In such cases, it is imperative to check for the presence of an imprint on the Endo medium after removal of suspicious colonies. The lab technician performs an oxidase test to confirm Gram and gas production. Isolated colonies of all types are sown on a medium with lactose with their obligatory incubation at a temperature of 37 ºС for one to two days. In the absence of isolated colonies, sieving on Endo medium is carried out by traditional bacteriological methods.
Conclusion
Analysis of tap water is carried out by various methods of qualitative and quantitative analysis. Such studies make it possible to evaluate the content in samples of substances of organic and inorganic origin that can have a negative effect on human he alth. If the MPC is exceeded, water is considered unfit for consumption.
