Old fashioned water pump pumping water up from a well digging.

What does water from a well contain, and how can I purify it?

There are dozens of options for purifying water from a well. It depends on what and how much you wish to purify and filter, as well as the purpose for which the purified water is to be used. How many requirements are set?


Purifying water from a well

When rain water seeps down through the layers of soil, it absorbs a large number of salts, which stays in the water when it is pumped up from the well. These salts are divided into cations and anions. 

Cations: Ca++, Mg++, Fe++, Na+, K+ and NH4+, H+, F3+

Anions: HCO3-, Cl-, SO4-- and also NO3- and NO2-

Some of these salts and minerals are removed during oxidisation, filtering and purification at the waterworks, before the water is pumped out into the pipe network as pure drinking water. The local waterworks may provide information on the salt and mineral content of the water in your area.

Water’s natural calcium content (Ca++) and magnesium content (Mg++) make the water “hard”. Hardness is measured in degrees of hardness (dH), in values of between 0 and 37º dH, where 0 denotes soft water.

When water is heated to over 55C, the materials become separated, and settle in the dishwasher and on glassware and other equipment. This means that lime scale builds up in the dishwasher, and the dishes are not washed clean from a chemical perspective.

Image showing the different levels water purification and it's agent


When should you use pure and purified water?

There may be many different reasons why you should use pure and purified water. For example:

The manufacture of products that must be clean (pharmaceuticals and biotechnology), and the results of analyses may be incorrect if water with unknown particles is used, but laboratory equipment, instruments and glassware must also be completely clean after washing. The same applies to autoclaves/steam sterilisers for hospital use.

Boilers and other types of equipment used for heating water, including disinfectors, have a much longer life span if they are supplied with soft water. Soap products are more effective and consumption can be halved if soft water is used, as well as the risk of the spread of infection through the water installation.


Measuring device

Depending on language and country: Micron, micrometre or µm. 1µ is a millionth of a metre or a thousandth of a millimetre (0.001 millimetre). A reversed osmosis membrane has pores or holes on one ten-thousandth of a µ (0.0001µ). The unit of measurement is a  micron, my or just µm. µm is often abbreviated to just µ.


What filtration method can we use, and how?

Human hair thickness


Smallest particle visible to the human eye


Smallest bacterium


Calcium carbonate molecule


Sea salt molecule






Microfiltration removes all bacteria.

from 0.1µ - 10,000µ

UV lighting


Ion exchange technology


Active carbon filter removes organic compounds, heavy metals, chlorine, etc. - not bacteria and viruses.

from 5 µ

Ultrafiltration is necessary for removing all viruses


Nanofiltration removes pesticides from ground water, heavy metals from waste water, removes nitrates, used for softening


Reverse osmosis pores/holes in membrane



Microfiltration – purify down to 0.1 µm

This enables us to remove particles, ochre, tastes and smells, but bacteria can also be removed with Microfiltration below 0.2 µm.

Bag filtration 05, µm to 1,200 µm.
Depth filtration 1µm to 200 µm.
Surface filtration 0.1µm – 100 µm.
MESH filtration 3 µm to 1,000 µm.


Active carbon filter - purifies water of smells and bad tastes.

Activated carbon can be used in the process of purifying waterActive carbon works wonders when it comes to removing toxins, smells and bad tastes from tap water. Active carbon filters are small pieces of carbon in granular or block form, which are treated to make them extremely porous. Just one gram of active carbon can easily have a surface area of 500-3,000 m2. It is this surface area that makes it possible for active carbon filters to be very effective at absorbing (removing) contaminated substances and other substances. Apart from the surface area, active carbon filters have different possibilities in relation to the size of the contaminated substances they remove.

When water passes through an active carbon filter, the chemicals are retained in the carbon.

The effectiveness depends on the water’s flow-through speed and temperature. Most small active carbon filters should therefore be used with low pressure and cold water. Active carbon is regular coconut shell, wood or coal, and is sold as granulated active carbon or carbon blocks.

Active carbon is very effective at removing at least 81 chemicals, fairly effective with a 30 other chemical substances, and moderately effective with a further 22 chemical substances. It cannot remove and purify everything from tap water.

According to the EPA (Environmental Protection Agency of the USA), active carbon is the only filter that is recommended to remove all 32 identified organic contaminated substances, including THMs. The same applies to all 14 pesticides and 12 herbicides.

Active carbon does not generally reduce TDS (total dissolved solids), which is a joint arrangement that is used by water filter dealers. More specifically, active carbon is not normally sufficient for the removal of the following substances.


UV treatment

Bacteria and micro-organisms in water can soon be rendered harmless by exposing the water to UV lighting. This method is both effective and environmentally friendly, as it does not involve the use of chemicals, and there are no bi-products.


Ion exchange technology

Lime (calcium and magnesium) can be removed from the water. Ion exchange technology takes advantage of the content of “loose” ions in water, e.g. Ca, Mg++ and negatively charged anions. By allowing the water to run over a surface containing a more active substance with an opposite charge, the ions will change place. The substance is coated on small plastic balls which are called granules or “resin” - although they have nothing to do with resin. Ion exchange systems are quite effective, and can purify and remove approx. 99% of the undesired salts.

Partial desalination (Dh 4-6)

In water softening, where calcium and manganese (cations) are removed, the result of the ion exchange is soft water, and the bi-product is sodium and carbon dioxide. Sodium salts do not form hard deposits. Carbon dioxide is a weak acid that can break down lime in old pipes.

Total desalination (Dh> 1/2)

When both cations and anions need to be separated out of the water, ion exchange containers are used. These remove the positively and negatively charged ions from the water. Some systems can even have both functions in the same container. This is called a mix bed.

The granule in the ion exchange system will “slide down” with time, as there is only a certain number of ions to exchange with. When the ion exchanger is used up, a cleaning and recharge is carried out - the container is cleaned of biofilm and impurities, and new ions are added in the form of salt. Some types of ion exchanger need to be regenerated by the manufacturer.


Ultrafiltration – purify down to 0.01 µm

Drinking water in Denmark does not usually contain bacteria that are pathogenic - as a well-known exception, Legionella can sometimes arise. This is dangerous because Legionella may cause very serious pneumonia, which weakened people could die of.

If the water is below 20o C, the bacterium is inactive, but at temperatures from 20° to 45°C Legionella develops rapidly. I.e. it flourishes in installations with warm used water, and it can spread via spray and water vapour. There are several ways of fighting the bacterium - e.g. the water can be illuminated with UV lighting, and if the warm water is over 60o C, the bacterium dies. Or ultrafiltration can be used, as the size of the virus is over 0.01 µm.


Nanofiltration – purify down to 0.001 µm

Nanofiltration removes pesticides from ground water, heavy metals from waste water, removes nitrates, and is used for softening.


Reversed osmosis – purify down to 0.001µm

A reverse osmosis filtration system is used when you need absolute pure waterRO water (Dem. water, desalinated water) is produced by filtering waterworks water through filtration columns, which only let small molecules such as water through. An RO installation is normally constructed from several units, so a filter captures the coarsest particles and ion exchanger takes the calcium and manganese before the water reaches the finer membranes, which thereby last longer.

Osmosis means that water moves along a semi-permeable membrane (that only the water can penetrate) in order to equalise a different concentration of dissolved substances. The water moves from the low to the high concentration “by itself” to achieve equilibrium.

In reversed osmosis, the water moves from a high to a low concentration. This doesn’t happen by itself, and the water should therefore be pressurised. Water molecules are among the smallest molecules found in liquid form.

Apart from the water molecules, the membrane can allow O2 and CO2 to pass through.
There is a water loss of around 10-15% of the water when reversed osmosis is used for the water treatment.

Conductivity is measured in µS/cm / TDS (PPM) can be connected to a CTS system, to enable the water quality to be monitored centrally. We recommend that PP pipes are used, with IR welding to the pipe network. If the pure water is to be drawn from a water fitting, the fitting must maintain the same level of purity.

You can find everything within Reverse Osmosis at our sister company Nordic Filtration here: Reverse Osmosis - Nordic Filtration

Reversed osmosis removes













Ultrapure water with EDI (electro-deionisation)

Hospitals, pharmaceutical companies and businesses in the food and electronics industry have replaced earlier installations with EDI systems in recent years. EDI splits the water with electricity, and in combination with ultrafiltration, water is achieved that is fully purified and pure - a water quality with a conductivity of < 0.2 µS/cm.

The big advantage of the EDI method is that the columns are regenerated by means of electricity, which makes an EDI system safe to operate and very easy to maintain.


Installation of filtration equipment

All types of water treatment systems must be installed by an authorised installer. The system naturally requires connection to water and electricity, and residual products must be discharged.

  1. Filter elements should be replaced as necessary or after 6 months.
  2. Osmosis systems must have membranes replaced.
  3. Ion exchange systems must be regularly supplied with salt.