How To Measure Water Purity

Four simple methods for evaluation of water purity

How to determine whether the drinking water is pure? Please read some simple ways to test water quality.

Total dissolved solids

The measurement of total dissolved solids (TDS) or salinity can show the level of inorganic ions dissolved in water.

Calcium, magnesium and sodium salts are the main components of TDS. High TDS levels are the most common pollutants which may cause harm in aquaculture.

Related： How To Measure TDS In Water

The Digital TDS meter with LCD screen is convenient for reading and recording data and storing readings, which is used to test the purity of the filter water quality to check the performance of your water filter and the hardness (1 grain = 17 ppm). The TDS tester is recommended for every family to ensure that you always drink clean and safe water.

Redox potential

Redox potential refers to the nature of disinfectants (such as chlorine) as solid oxidants. Strong oxidants can burn viruses, bacteria and other organic substances to keep the microbial level of water in a safe state.

When the ORP value is equal to or more than 650mv (MV), water quality is good.

A low ORP value (e.g. 250Mv) indicates that the disinfection capacity of chlorine may not be enough.

ORP meter can be used to appropriately measure chlorine content in water.

Related： How To Measure ORP In Water

Microbial contamination detection

When testing water quality, it is essential to evaluate the total coliform bacterial count because it can cause disease when there are high levels of bacterial count in water. We can evaluate the total number of bacteria by plate counting to reflect the water quality sanitation. If there is poor water sanitation, bacteria will quickly increase in value and spread. We should always test water quality when:

• Maintenance of water supply system
• Insufficient water pressure in the water supply system
• Human or animal infection with water-borne diseases
• Low breeding production
• When the change in colour, smell or taste
• Well side overflow

PH measurement

PH measures the number of hydrogen ions in the solution, which ranges from 1.0 to 14.0, where 7.0 is neutral.

pH below 7.0 indicates acidity, while PH above 7.0 indicates alkalinity.

pH value higher than 8.0 will make the water bitter, thus affecting the taste.

We can reduce water’s high pH value by using inorganic acids. However, the organic acid is a negative impact on drinking water.

PH will affect the water quality and the effectiveness of disinfectants (such as chlorine).

When the pH is higher than 8.0, chlorine mainly exists in the form of fluorine ions with low disinfection efficiency. The ideal pH value of drinking water for disinfection is between 5 and 6.5.

We should measure water quality regular, use sterile containers to collect samples at the front of the water supply and the end of the water line, and analyze them in a certified laboratory. When taking water samples, the most important thing is not to pollute the water samples.

How to measure the purity of water in the laboratory?

Pure water is essential when working in the laboratory, but the purity of water depends on the composition of the soluble electrolyte solution in the water. Generally, there is a tiny amount of Na, K, Ca, Mg, Ca, Cl, and other positive ions in the water.

The greater the concentration of this ion in the water, the higher conductivity. Conversely, the higher the purity of water, the smaller the ion concentration and the smaller conductivity. Therefore, if you want to know the purity of water, you can measure its conductivity in water.

Measurement method of pure water conductivity

There are two common methods to determine the purity of water quality:

• chemical composition analysis
• conductivity method.

The chemical analysis method can accurately measure water’s composition and various residues. However, its operation and analysis are complex, so it is unsuitable for rapid pure water quality on-site.

At this stage, the conductivity meter is widely used to measure the purity of water. It has the advantage of faster speed and convenience and so on.

The conductivity of water reflects the total output of carbonate in water, which is an important index value for detecting water purity. The smaller the conductivity of water, the higher the purity of water.

How to use conductivity meter to test water purity?

Conductivity is the ability of an object to conduct current. The measuring principle of the conductivity meter is to put two parallel plates into the measured solution, add a certain potential to both ends of the plates, and then measure the current flowing between the plates.

According to Ohm’s law, conductivity (g) – the reciprocal of resistance (R) is determined by the conductor. The basic unit of conductivity is Siemens (s), also called Ohm, because the geometry of the conductivity cell affects the conductivity value, which is expressed in unit conductivity s / cm to compensate for the differences caused by various electrode sizes in the standard measurement.

The conductivity of water is related to the amount of inorganic acid, alkali and salt it contains. When their concentration is low, the conductivity increases with the increase of concentration. Therefore, this index is commonly used to speculate ions’ total concentration or salt content in water.

There are different conductivity for different types of water.

• The conductivity of fresh distilled water is 0.2-2 μ S / cm, but it increases to 2-4μ S/cm due to the absorption of CO2 after being placed for a while； 
• The conductivity of ultrapure water is less than 0.10/ μ S/cm； The conductivity of natural water is 50-500 μS / cm ；
• The conductivity of mineralized water is 500-1000 μ S/cm； 
• The conductivity of industrial wastewater is more than 10000 μ S/cm due to the water containing acid, alkali and salt； 
• The conductivity of seawater is about 30000 μ S/cm;

We commonly determine the electrode constant by standard solution with known conductivity. The conductivity of the solution is related to its temperature, polarization phenomenon on the electrode, electrode distributed capacitance and other factors.

Generally, conductivity tester with compensation or elimination device. The water sample should be determined as soon as possible after collection. It must be filtered or extracted if it contains coarse suspended substances, oil and grease, which interfere with the determination.

Instruments and reagents for conductivity test of pure water

1. Conductivity meter2. Platinum black conductivity level3. Thermometer4. Small measuring cup5.0.001mol. L-1kcl saturated solution6. Pure water

Steps:

1) Connect the power supply of the conductivity meter, clean the platinum black conductivity level with deionized water and suck it away with filter paper, heat the constant temperature water bath, and adjust the temperature of the constant temperature water bath to 25 ℃. Moreover, the conductivity meter must be zeroed before use.

Clean the conductivity cell with deionized water 2-3 times, wash it twice with 0.0200mol L-1 KCL wastewater, wash it once with 0.0200mol l-1kcl saturated solution, and then pour the wastewater into the collection bottle.

Pour the KCl saturated solution into the conductivity cell at an electrical level. When it swallows, the electrical level is better. Put the conductivity cell into a 25 ° thermostatic water tank, and receive the electrical level transmission line into the conductivity meter. After the temperature in the conductivity cell is balanced with the temperature of the thermostatic water tank, we can accurately measure the conductivity of the KCl saturated solution.

2) Clean the conductivity cell with the water sample and accurately measure the conductivity of purified and drinking water, respectively. Record each value once. Generally, the deviation is slight when the instrument needle is in the middle. If the deviation of the instrument needle is too small or large, it can be adjusted according to the switch.