WATER SAMPLING

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“Why sample and test the water?” • To help ensure you are using water suitable for your in-

tended agricultural use.• To help ensure that your drinking water is safe.• To help determine the effectiveness of your water treat-

ment system.

TYPES OF SAMPLEGRAB SAMPLE AND COMPOSITE SAM-PLE

1. GRAB SAMPLE

A grab sample is a single water sample collected at one time from a single point. A grab sample represents only the composition of the water at the time and place the sample was collected.

Grab sampling is suitable when:• analyzing situations at specific sites (e.g. maximum

density of coliform bacteria at a bathing beach).• analyzing for unstable parameters that have to be mea-

sured right away or on site, e.g., Dissolved Oxygen (DO), temperature, pH, Total Dissolved Solids (TDS), salinity, etc.

• a snapshot of water quality at a particular instant is de-sired

• the characteristics of the waters are known to be rela-tively constant over time

• collecting samples to be analyzed for parameters that could be adversely affected by compositing process.

2. COMPOSITE SAMPLE

• The Philippine National Standards for Drinking Water (PNSDW) of 2007 defines composite sample as a series of individual grab samples taken at different times from the same sampling point and mixed together. A composite sample may also be a number of grab samples of equal or weighted volumes mixed in one container.

Composite samples are preferred when:• assessing the total concentration of a substance or pollu-

tant in water (e.g. total phosphorus potentially available for phytoplankton growth) or the population of an organ-ism (e.g. the size of a bacterial population).

• the variables to be assessed are unevenly distributed.

SAMPLING BOTTLES

• The specific sample bottles required for the type of test-ing you request will be provided to you by the laboratory. They are usually well labeled as to the type of sample they are to contain as well as any special instructions necessary. Ask the laboratory staff if you have any ques-tions regarding filling the sample bottles and the preser-vation techniques required for the different types of bot-tles. You can also ask the laboratory if it is possible to use your own sample bottle that you may have available at the time depending on the tests that you require.

Shipping of Samples

• Once water samples are collected, they must be transported to the labora-tory immediately. The mode of transportation will depend on the geo-graphic location and maximum allowable time lapse before analyzing each parameter. Usually they will require them within 24 hours of the time they were sampled.

• Before shipping, always check that all sample bottles recorded on the field sampling sheets have been placed in the cooler or carton. Samples must be shipped in a dark, cool environment using cold packs or melting ice. The samples should never be allowed to freeze as this can cause irreversible separations and reactions in the water. Shipping labels which clearly iden-tify the source and destination of the samples will increase the transporta-tion efficiency.