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. Open water pollution is associated with the activities of industrial enterprises, transport, human activities.
Important aspects
It is necessary to have an idea of the main pollutants of drinking water that negatively affect human health. 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 research results, about 75 percent of the samples pose a threat to human health, and in 12% a significant excess of the concentration of toxic compounds was found.
The quality of drinking water is undoubtedly an urgent and serious problem of our time, therefore the chemical analysis of tap water is so important.
Quality indicators
They are divided into several groups:
- organoleptic, which include smell, turbidity, color;
- chemical (includes various chemical compounds);
- microbiological.
The color of water is due to the presence of complex compounds of iron, it is measured visually. The smell of water is given by volatile substances that fall into it together with waste water. The cause of the turbidity is considered a variety of finely divided substances. The source of smack of tap water can be organic substances of plant nature.
Chemical classification
In order to analyze tap water, you need to know the basic chemical compounds that may be included in it.
The components of the chemical composition are divided into six groups:
- The main ions (macrocells), which include potassium, magnesium, calcium cations. They make up 99.98% by weight of all salts dissolved in water.
- Dissolved gases (oxygen, hydrogen sulfide, nitrogen, methane).
- Nutrients are compounds of phosphorus and nitrogen.
- Trace elements are metal ions that are found in small quantities.
- Dissolved organic substances, which include alcohols of the limit and unsaturated series, aromatic compounds, hydrocarbons, as well as nitrogen-containing compounds. When assessing their quantitative content, permanganate or dichromate oxidation of water (COD) is calculated, as well as biochemical oxygen consumption.
- Toxic pollutants - heavy metals, petroleum products, organochlorine compounds, phenols, synthetic substances (surfactants).
Evaluation Options
The analysis of tap water involves the determination of the following characteristics:
- The content of salts in it (in terms of calcium bicarbonate).
- Alkalinity of water. It is determined by titration of a water sample with a strong acid, for example, hydrochloric acid, in the presence of phenolphthalein (pH of the color transition is 8.3), then methyl orange (pH of the transition 4.5).
- Oxidation. For drinking water, it cannot exceed 100 mg / l (permanganate method).
- Hardness of water. The hardness is determined by the number of millimole equivalents of calcium and magnesium ions contained in 1 l of water (mol / l). For drinking purposes, use water having medium hardness.
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 a clean conical flask, then one milliliter of potassium chromate is added. One sample is titrated with a solution of silver nitrate until a faint orange hue is detected, the second is used as a control sample. Next is the processing of results, comparing them with tabular data.
Water hardness analysis
Let's try to understand how to make an analysis of tap water in order to identify its hardness. According to the methodology, 100 ml of filtered tap water is added to a conical flask. Then add 5 ml of buffer solution, then 5-7 drops of chromogen-black indicator and titrate with vigorous stirring with 0.05 N Trilon B solution until a stable blue color appears. Next is the processing of the results, comparing them with acceptable standards.
Determination of bacteria using titrimetric analysis
Having found out where you can make a tap water analysis, let's try to understand how to determine the presence of bacteria in tap water samples.
The titration method is suitable in cases where there is no required equipment and materials to conduct membrane filtration. It is based on the formation of bacteria after sowing a certain amount of water in a nutrient liquid medium, followed by reseeding them on a special nutrient medium with lactose. Further identification of the colonies by cultural and biochemical methods.
In the study of tap water by a qualitative method (suitable for routine sanitary surveillance, production control) three volumes of a sample of one hundred milliliters are seeded.
Each volume of the analyzed water is inoculated into a lactose-peptone medium. Sowing of 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 ° C for one or two days. Not earlier than after a day of incubation, a preliminary assessment of the samples is carried out. In tanks where turbidity is detected, gas is observed, and a bacteriological loop is sown on fragments of the Endo medium, thereby obtaining isolated colonies. Tanks without signs of growth are left in the thermostat and again analyzed after two days. Crops that do not have signs of growth are called negative, they are not used for subsequent studies.
Of the containers in which gas formation was detected, turbidity appeared, or there is one of these signs, crops are sown on Endo medium sectors. Crops on the Endo medium are incubated at 37 ° C for 18-20 hours. When turbidity and gas are detected in the accumulation medium and the colonies on the Endo medium increase, which are characteristic of lactose-positive bacteria of dark red or red, having a metallic luster (no luster), convex with a red center and an imprint on the nutrient medium, the presence of common coliform samples in this volume bacteria.
The presence of the design bureau must be further experimentally confirmed. If only turbidity was revealed in the accumulation medium, then belonging to lactose-positive colonies is a dubious fact. In such cases, be sure to check for the presence of a fingerprint on the Endo medium after removal of suspicious colonies. The lab technician performs an oxidase test to confirm Gram affiliation as well as gas-forming ability. Inoculate isolated colonies of all types on a medium with lactose and carry out their mandatory incubation at a temperature of 37 ° C for one to two days. In the absence of isolated colonies, sieving on the 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 health. If the MPC is exceeded, water is deemed unsuitable for consumption.