from mkgupta

1. Water Sampling
The process of collecting a representative portion of water, as
from the natural environment or from an industrial site, for the
purpose of analyzing it for constituents
The process of taking a portion of water for analysis or other
testing. e.g. drinking water to check that it complies, or river
water to check for pollutants, or bathing water to check that it
is safe.

2. Objective
primary goal of water sampling is to observe and measure how
water quality changes over time.
An important premise to water sampling work is that high acidity or
high alkalinity (pH levels) in the water might be normal for a given
environment or ecological region
water samples must be taken and analyzed repeatedly over a
period of weeks, months, years, and decades to determine more
precisely how water conditions change.

3. Water Sampling Procedure
1. If sampling a body of running water, point the mouth of the bag upstream and your
hands dwnstream to avoid contamination.
2. If sampling from a water faucet, run the faucet for 1 minute before obtaining a sample.
3. Rinse the bag twice with the sample water prior to filling and closing.
4. Fill bag as full as possible. Half-filling the bottle leaves more room for oxygen which
will promote degradation of your sample.
5. Collect data such as temperature and pH which affect the solubility of many ions.

4. Sampling Methods
If an environmental domain was completely homogeneous, a
single sample would adequately represent it. However, we
seldom come across such a situation, as the environment is
highly heterogeneous.
A static system is one which does not change much with time.
It must be sampled so that the sample reflects all the
inhomogeneity of the system. If a field is to be tested for a
longlived pesticide in the soil, that could be considered to be
relatively static system.
A dynamic system is one whose content changes with time.
Most regions which we wish to characterize by taking samples
are dynamic to some extent, and show both spatial and

5. Methods of water sampling
 Systematic
 Random
 Judgmental (nonstatistical)
 Stratified
 Haphazard

6. Systematic Sampling :
Systematic sampling, where points are selected at regular and even
intervals, is statistically unbiased- providing the coordinates of the
sampling points are determined by random numbers. Systematic
sampling does not generate clusters of sampling points and is easier
use to survey sampling locations than random sampling. A square grid
is the commonest type of systematic sampling pattern.
For example , The area to be analyzed may divided by a grid, and a
sample taken at each point of the grid. For air pollution studies, an air
sample might be taken at fixed intervals of time, say every three
This approach does not require the prior knowledge of pollutant
distribution, is easy to implement, and should produce unbiased
samples. However, systematic sampling may require more samples to
be taken than some of the other methods.

7. Random Sampling : with random sampling, sampling points are selected
randomly- but not arbitrarily. A legitimate “random number generator”
should be used to determine sampling point coordinates. Most scientific
calculation can generate number that are sufficiently random for
purpose. The randomisation process ensures any location within the
sampling area has an equal chance of being selected as a sampling
While random sampling is statistically unbiased, sampling points , by
chance, can cluster together. This makes them deficient for detecting
spots and for giving an overall picture of the spatial distribution of the
contamination. In practice, random sampling has limited use in
contaminated site investigation. For example. area to be sampled is divided into
triangular or rectangular areas with a grid. Three dimensional grids are used if the
variation in depth (or height) also needs to be studied. The grid blocks are given
numbers. A random number generator or a random number table is then used to select
the grid points at which samples should be collected. If a waste site contains numerous
containers of unknown wastes and it is not possible to analyze every container, a

8. Judgemental sampling
For this method, sampling points are selected on the basis of the investigator’s knowledge of the
probable distribution of contaminants at the site. It is an efficient sampling method which makes
use of the site history and field observation but has a disadvantage of being potentially biased.
The quality of the sampling results depend on the experience of the investigator and the
available site history information. Judmental sampling should not be used in validation sampling.
In the lake samples might be collected just around the outfall point. This type of judgmental
sampling introduces a certain degree of bias into the measurement . E.g. it would be wrong to
conclude that the average concentration at these clustered sampling points is a measure of the
concentration of the entire lake. However, it is the point which best characterizes the content of
waste content of the waste stream. In many instances, this may be the method of choice,
especially when purpose of the analysis is simply to identify the pollutants present. Judgmental
sampling usually requires fewer samples than statistical methods, but the analyst need to be
aware of the limitation of the samples collected for this method.

9. Stratified sampling
First divide the site into sub-areas according to geological and geographical features,
nature of the contamination, former uses pattern of the site, intended future use of
the sub areas, and other relevant factors. Each sub area can then be treated as an
individual site and different sampling patterns and sampling densities applied. A
stratified sampling pattern approach is best suited to investigation for large sites with
complex contaminants distributions. This sampling patter may require a more complex
statistical analysis. It is not considered further here.
The strata in a stratified scheme do not necessarily have to be obviously different. The
area may be divided into arbitrarily sub areas. Then a set of these are selected
randomly. Each of these units is then sampled randomly.
e.g. a hazardous waste site can be divided into different regions or units. Then, the soil samples are
collected at random within each region or within randomly selected regions. Stratification can reduce
the number of samples required to characterized an environmental system, in comparison to fully
random sampling.

10. Haphazard sampling
A sampling location or sampling time is chosen arbitrarily. This type of sampling is
reasonable for a homogeneous system. Since, most environmental system have
significant spatial or temporal variability, haphazard sampling often led to biased
results. However, this approach may be used as a preliminary screening technique to
identify a possible problem before a full scale sampling is done.