Collecting and preserving water samples - field methodology

Methods guide · June 17, 2026

Some of the most important indicators - nitrogen, phosphorus, metals, many forms of pollution - are hard to measure at the water itself. Those determinations are done by a laboratory. But there is a truth that anyone working in the field learns quickly: a lab result is worth exactly as much as the sample you brought in. The best instrument will not fix badly collected water.

That is why sampling is a skill worth valuing - and one you can see in experienced researchers: calm, methodical movements, a clean bottle rinsed with river water, a precise label, a cool box in the backpack. Students, monitoring staff, researchers and citizen-science groups who do it properly give the lab honest material - and give themselves credible data. It is a modest but fundamental part of good fieldwork.

A representative sample - meaning what

The sample should reflect the water you are asking about - not a random nook by the bank:

• Sample in the current / mixed zone, away from stagnant pockets and stirred-up sediment.
• Set the depth/point to match the aim of the study (surface, a specific depth, a depth-integrated sample).
• Do not stir up the bottom - sediment suspension can distort phosphorus and metals, among others.

Container and filling

• A clean bottle suited to the determination (for nutrients/metals usually plastic, for some organic compounds - glass; for metals acid washing may be required).
• If the sample contains no preservative - rinse the bottle with the water being tested before filling.
• Fill according to the requirement of the determination (some parameters - to the brim, no air bubble; if freezing, leave room for expansion).

Preservation

Most samples must be preserved straight away in the field, otherwise the composition changes on the way:

• Cooling (about 4°C, in the dark) - the basic treatment for most determinations.
• Acidification - e.g. with acid to pH < 2 for nitrogen/nutrient forms, separately for metals - as required by the method.
• Field filtration - when you are interested in the dissolved fraction.

The choice of preservative depends on the specific indicator - this is settled in advance, per the methodology.

What each determination requires

The requirements are easier to remember side by side than in prose - and the rows differ more than one expects. This is an orienting cheat sheet: agree the details with the laboratory, because container, preservative and time depend on the method used.

⚠️ An exceeded holding time invalidates a result just as thoroughly as no preservation does - and unlike a forgotten bottle, nothing shows it. That is why fieldwork is sequenced from the shortest time: measurements on the spot first, then microbiological samples, and last those that will survive the journey.

Labelling, transport and time

• Label and note: place, date, time, indicators to be determined, sampling conditions.
• Transport fast and cool.
• Holding time - every determination has a maximum allowable time from collection to analysis; exceeding it invalidates the result.

The most common mistakes

• Contaminating the sample (hands, a dirty bottle, insect repellent on your hands).
• An unrepresentative point - by the bank, in a stagnant pocket, with stirred-up sediment.
• No preservation / poor cooling - the composition “escapes” on the way.
• Exceeded holding time or a wrong label - common, and costly.

How often

Sampling is carried out in fixed campaigns (e.g. monthly/seasonal) and from the same sites - only comparable series reveal nutrient and load trends. Consistency of method matters more here than frequency.

Sources and further reading

The methodology of sampling and preservation is described in the PN-EN ISO 5667 series of standards (water sampling) and in GIOŚ materials. The specific requirements (container, preservative, time) depend on the indicator being determined - it is worth settling them with the laboratory before you set out.

How to make it easier

Sampling itself is only the beginning - then you have to link each sample with its place, time and lab result, and keep it in order across successive campaigns. This is where it is easiest to make a mess: bottle numbers on tape, results in a separate file weeks later.

LimnoLog ties it all together:

• in the field you record the fact of sampling - the station, date, time, conditions (also offline);
• when the lab results arrive, you add the values to the same session - nitrogen, phosphorus and other indicators land next to the right sample, not in a disconnected spreadsheet;
• a series and a chart emerge from the campaign - loads and nutrient trends are visible at once;
• the data you can share via a link or export.

And because LimnoLog accepts any indicator - from those measured on the spot to laboratory ones - you have one consistent place for the whole picture of your water.

Early users get free access for now and keep their features for good. If you carry out water sampling - take a look and try it.