Bacteria and Viruses in Water - Microbiological Contamination and Prevention Methods

Water can be completely clear, have no unpleasant odor or taste, and still contain microorganisms undesirable for health. This is precisely what distinguishes microbiological contamination from many other water problems - its detection by external signs alone is often impossible.

Various types of bacteria, viruses, protozoa, and other microorganisms can enter water. Some of them are quite common in the natural environment, but the presence of pathogenic microorganisms already poses a risk related to water safety.

Special attention is needed for borehole, natural spring, reservoir-stored, and other individual water sources, as the microbiological condition of such water can change with variations in environmental conditions.

The latest WHO (World Health Organization) recommendations for drinking water quality consider water safety from the source to the end-user using a risk management principle and identify microbiological hazards as one of the main directions for drinking water quality.

What is microbiological water contamination?

Microbiological contamination means the presence of microorganisms in water that, under certain conditions, can have a negative impact on health.

Possible microbiological contaminants found in water include:

• E. coli
• Salmonella
• Campylobacter
• Shigella
• Norovirus
• Hepatitis A
• Giardia
• Cryptosporidium

The size, structure, and behavior of these microorganisms in water differ significantly. That is why one type of filtration cannot be equally effective against all microbiological risks.

For example, parasites and protozoa are relatively large, bacteria are smaller, and viruses are even smaller. Accordingly, the capability of a specific membrane or filter primarily depends on its technology, pore size, and confirmed filtration characteristics. In the CDC's water filtration guide, the capabilities of microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are distinguished precisely by this principle.

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How do bacteria and viruses enter water?

The cause of microbiological contamination is not always the same. Depending on the type of water source and environmental conditions, contamination can arise in the natural environment as well as in the water storage and distribution system.

Common causes include:

• Surface water entering a well or spring;
• Heavy rainfall and flooding;
• Malfunctioning sewage system;
• Proximity of a septic tank;
• Animal waste;
• Organic and biological material entering the water;
• Runoff from agricultural areas;
• Damaged or improperly constructed well structure;
• Contamination of a water reservoir;
• Damage to the pipeline;
• Inadequate sanitary conditions in the water system.
  

In the case of well water, the condition can be stable for a long period and then change, for example, after heavy rain, flooding, construction work, or changes in groundwater conditions.

Therefore, a water source that has been used problem-free for years does not automatically mean that its microbiological condition will always remain unchanged.

Water may look clean but still be contaminated

The presence of bacteria and viruses does not always cause changes in water color, odor, or taste.

Microbiologically contaminated water can:

• Be completely clear;
• Have no unpleasant odor;
• Have a normal taste;
• Leave no sediment;
• Have a normal TDS reading.

TDS is not an indicator of microbiological safety.

A TDS meter assesses electrical conductivity related to the total amount of dissolved substances in water but does not determine the presence of bacteria or viruses.

Therefore, the visual condition of water, taste, odor, or TDS cannot replace a microbiological analysis.

Microbiological water analysis

Laboratory analysis is used to assess microbiological conditions.

In practice, not all possible pathogens are individually searched for. Instead, specific indicator parameters are used to assess the sanitary condition of the water.

Total Coliform

Coliform bacteria are widespread in the environment. Their detection does not always indicate fecal contamination itself, but it can point to a problem with the sanitary condition of the water source, well, reservoir, or distribution system.

E. coli

E. coli is a much more important indicator when assessing fecal contamination.

If E. coli is detected in water, attention is needed not only for final filtration but also for identifying the primary source of contamination - for example, checking the well structure, septic system, reservoir, or other possible sources.

For private wells, the EPA recommends testing for total coliforms at least once a year. Additional testing is especially important after flooding, well repair, or noticeable changes in water conditions.

How is water protected from bacteria and viruses?

Here's one of the most important distinctions:

Not all water filters are designed for microbiological protection.

For example, the main purpose of an activated carbon cartridge may be to reduce chlorine, unpleasant taste, and odor. A mechanical cartridge, on the other hand, traps sand, rust, silt, and other solid particles.

Neither of them automatically provides a full microbiological barrier against bacteria and viruses.

For microbiological protection, the following are mainly used:

UV disinfection, appropriate membrane filtration, or a combination of several technologies.

UV - Ultraviolet Disinfection

UV is one of the most common methods for microbiological water treatment.

Water passes through a special chamber in the system, where it is exposed to ultraviolet radiation. Under appropriate UV doses, the genetic material of microorganisms is damaged, and they lose their ability to reproduce and spread infection.

UV technology is used for:

• Bacteria;
• Viruses;
• Control of various protozoa and other microorganisms.

Its significant advantage is that no disinfectant chemicals are added to the water.

However, water quality is very important for effective UV disinfection.

Why does a UV system need pre-filtration?

Sand, silt, rust, and other suspended particles can reduce the effectiveness of UV radiation and partially "shield" microorganisms from the light.

Therefore, appropriate mechanical pre-filtration is often used before the UV system.

In the CDC's water treatment overview, UV systems with pre-filtration are described as a more effective option for controlling microorganisms.

What does UV not do?

UV disinfection is not chemical water filtration.

UV itself does not remove:

• Water hardness;
• Calcium and magnesium;
• Dissolved salts;
• Iron;
• Manganese;
• Nitrates;
• Other dissolved chemical contaminants.

Therefore, if several problems exist in the water simultaneously, UV becomes one stage of a complete treatment system, not the only device.

Ultrafiltration - UF

Ultrafiltration is a method of membrane filtration.

Water passes through a membrane whose microscopic pores physically trap particles and microorganisms of a certain size.

The pore size of typical UF membranes is approximately in the 0.01 micron class, although the specific value varies by model.

Ultrafiltration is effective for:

• Bacteria;
• Parasites like Giardia and Cryptosporidium;
• Trapping other relatively large microorganisms and particles.

In the case of viruses, it is essential to consider the technical data of the specific membrane.

According to CDC classification, typical ultrafiltration removes bacteria and parasites, while the ability to remove viruses may be partial. Accordingly, the name "UF" alone does not imply complete effectiveness of a particular system against all viruses.

Reverse Osmosis - RO

Reverse osmosis is a technology for deep membrane water treatment.

In an RO system, water passes through a very fine membrane under pressure. The filtration scale of a typical RO membrane is approximately 0.0001 microns.

This technology creates an effective membrane barrier for:

• Parasites;
• Bacteria;
• Viruses.

At the same time, RO also reduces many dissolved substances in the water, including various salts and chemical components depending on the specific system and membrane.

Therefore, reverse osmosis is often used for deep filtration of drinking water when the goal is not just to reduce mechanical or microbiological contamination.

Even with RO, the final effectiveness depends on the specific system, the condition of the membrane, water pressure, correct installation, and maintenance.

Mechanical Filtration

The function of a mechanical filter is different.

Its main task is to retain solid particles present in the water, for example:

• Sand;
• Rust;
• Silt;
• Particles from pipes;
• Various types of sediment.

A standard mechanical filter is not a substitute for microbiological disinfection.

Nevertheless, mechanical filtration plays an important role in the operation of a complete system, especially before UV disinfection.

Municipal Water and Microbiological Protection

Municipal water undergoes treatment and disinfection stages in a water treatment plant. For disinfection, chlorine, chloramine, UV, ozone, or other technologies may be used depending on the system's specifics.

At home, the purpose of additional filtration may be:

• Additional membrane filtration of drinking water;
• Chlorine reduction;
• Improvement of taste and odor;
• Creation of an additional microbiological barrier;
• Resolution of other specific problems.

In such cases, it is possible to use an appropriate UF or RO system - according to specific needs and desired filtration depth.

Microbiological Protection of Wells and Natural Springs

For wells and natural springs, the approach is different because the water composition directly depends on the specific source and environmental conditions.

The selection of the correct system begins with water analysis.

A typical treatment scheme might look like this:

Water analysis → Mechanical filtration → Necessary chemical treatment → UV disinfection

For example, if high hardness, iron, and microbiological risk are simultaneously observed in the water, installing only a UV system will not solve the remaining problems.

In such a case, it may be necessary to:

Mechanical filtration → Iron removal → Water softening → UV disinfection

The specific sequence is always determined by the actual water analysis.

For drinking water lines, it is also possible to use an additional UF or RO system.

Why is regular maintenance important?

Filtration and disinfection systems work effectively only under proper operating conditions.

Depending on the system type, periodic maintenance is required:

• Changing pre-cartridges;
• Monitoring membrane condition;
• Replacing the UV lamp;
• Checking and cleaning the quartz sleeve;
• Monitoring the sanitary condition of the reservoir;
• Periodic disinfection of the system if necessary.

A UV lamp may still glow visually, but its effective UV radiation decreases over time. That's why the replacement period is determined by the specific manufacturer's technical recommendations, not just the visual condition of the lamp.

In the case of membrane systems, timely maintenance of cartridges and membranes is also important, as a contaminated or damaged element reduces the system's effectiveness.

One Filter or Several Treatment Stages?

There is practically no universal water treatment system.

For one water, the main problem might be mechanical contamination; for another, hardness; for a third, iron; and in other cases, several problems and microbiological risks might be present simultaneously.

That is precisely why an effective system is created for specific water.

Water analysis → Identification of problems → Selection of appropriate technologies → Correct sequence → Periodic control

This approach is much more reliable than choosing one specific filter based only on a general product description.

Key Takeaways

Water that looks clean does not always mean it is microbiologically safe.

Bacteria and viruses may not change the color, smell, or taste of water at all. Therefore, in the case of well water and natural springs, the most reliable basis for assessing microbiological safety is laboratory analysis.

It is also important to differentiate between various technologies:

• Mechanical Filtration - Removal of solid particles;
• Activated Carbon - Primarily for chlorine, taste, and odor correction;
• UF - Membrane barrier for bacteria and larger microorganisms;
• RO - Deep membrane filtration, including against bacteria and viruses;
• UV - Microbiological disinfection of water.

In case of a microbiological problem, the main thing is not simply the existence of a "filter," but rather the correctly selected technology and the proper functioning of the entire system.

At Aquarea, a water treatment system can be selected according to the water source, laboratory analysis, and required output - for drinking water, as well as for well water, natural springs, and whole-house water treatment.

Source: CDC - Guidelines for Testing Well Water · EPA - Protect Your Home’s Water