The collection, preservation and determination of water quality indicators are important aspects of environmental monitoring and water quality evaluation. Proper sampling and preservation methods can ensure the quality of water samples prior to analysis, resulting in accurate and reliable WQO data. The following are the basic methods for water sample collection, preservation and water quality index determination:
Water sample collection.
1.*Sample Preparation**:
Choose the appropriate sampling container, usually using glass bottles or high-density polyethylene bottles.
Containers should be thoroughly washed and dried before use, or washed with sample water.
Avoid using detergents that contain potential contamination of the sample.
2.*Sample Point Selection**:
Sampling points are selected according to the monitoring purpose and water quality investigation requirements.
Sampling sites should be representative and reflect the overall water quality status of the waters being monitored.
3.*Sampling Method**:
Avoid sampling immediately after rainfall to reduce the impact of surface runoff on water samples.
Care should be taken to avoid mixing surface, middle and bottom water when collecting surface water.
Use a sampler or draw water directly from a source, ensuring that the sampler or container does not contaminate the water sample.
4.*Sample Size**:
The amount of sampling is determined based on the needs of the analytical test, and it is often necessary to collect enough samples for multiple analyses.
5.*Sampling Log**:
Record field parameters such as sampling time, location, weather conditions, water temperature, pH value, etc.
Water samples are preserved.
1.*Refrigerated**:
Many water quality parameters (e.g., dissolved oxygen, BOD, microbial indicators) are more stable at low temperatures.
Samples should be refrigerated as soon as possible after collection, keeping below 4 °C.
2.*Protected from light**:
Some water samples are light-sensitive and should be protected from light, using a brown glass bottle or wrapping a transparent container in aluminum foil.
3.*Antiseptic Treatment**:
For water samples that require metal content determination, it may be necessary to add preservatives such as nitric acid or hydrochloric acid immediately after sampling.
4.*Avoid***
Strenuous ** should be avoided during transport to prevent sample deterioration.
Methods for determining water quality objectives.
1.*Physical Indicators**:
Color, turbidity**: Determined using a colorimeter or turbidity meter.
Temperature**: Measured with a thermometer.
Conductivity**: Determined using a conductivity meter.
2.*Chemical Indicators**:
pH**: Measured using a pH meter.
Dissolved oxygen (DO)** is determined using a dissolved oxygen meter.
Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD)** were determined by laboratory standard methods.
3.*Biological Indicators**:
Escherichia coli**: Determined using standard plate counting.
Total number of bacteria**: Colony counting was performed using nutrient agar plates.
4.*Toxicity Indicators**:
Heavy metals**: Determined by atomic absorption spectrometry, atomic fluorescence spectrometry, or inductively coupled plasma mass spectrometry.
Organic contaminants**: Determined by gas chromatography, liquid chromatography, or gas chromatography-mass spectrometry.
When determining water quality indicators, relevant national standards or industry standards should be followed to ensure the accuracy and reliability of analytical methods. At the same time, in order to obtain accurate results, it is recommended to calibrate the analytical equipment on a regular basis and participate in inter-laboratory comparisons and proficiency testing activities.