Do I need to treat my water?

Do I need to treat my water?

Why should I treat my water? 

Raw water and municipal primary treatment

Most people in developed countries get their water from municipal sources. The water either origins from groundwater or surface water (lakes, rivers, and creeks) and is called raw water or source water. Raw water is, with some exceptions, unsuitable for human consumption and needs to be treated. 

Ground water often contain less contaminants than surface water, but both types of water typically go through primary treatment at the municipal water works. The primary treatment can consist of different steps depending on the level of minerals, particles, bacteria, and parasites it contains. 

Common treatment steps may include:

  • filtering 
  • chemical precipitation
  • pH-adjustment
  • infiltration or groundwater recharge
  • aeration 
  • disinfection

The disinfection is often accomplished with UV light and/or dosing of a disinfectant chemical such as chlorine. In Sweden for example, 88% of water works for surface water and 62% of water works for ground water have UV installed as a microbiological barrier. 

In addition to the disinfection at the water works, some countries also apply a chlorine residual in the distribution network, which means that the added amount of chlorine at the water works is greater than what reacts with the contaminants at the water works premises. Consequently, there is a chlorine residual in the distribution network and its concentration decreases from the water works to the far extremities of the supply network. As a general rule, chlorination is efficient against viruses and some bacteria, whereas disadvantages include negative health effects of chlorination by-products, added undesirable taste and odor to the water and is less efficient to certain bacteria and protozoa (e.g., cryptosporidium and giardia). 

The Netherlands is one of the few countries where chlorine is not used at all, neither for primary disinfection nor to maintain a residual disinfectant in the distribution network. E. coli monitoring data from the distribution network do not show a significantly lower number of detections in chlorinated systems. Data from the UK indicated 0.03 to 0.04% of the (chlorinated) drinking water samples from the distribution 15 network were positive for E. coli, and in France 0.4 to 1.0% of the samples contained coliforms (no data on thermotolerant coliforms or E. coli) (van Lieverloo et al., 2007a). In the Netherlands 0.1% of the samples from distribution systems without disinfection were positive for E. coli or thermotolerant coliforms. 

Private wells and surface water

Municipal water from a water distribution network is not available to everyone. In Sweden 1,2 million people get their water in their permanent homes from private wells (or surface water), and an equal number of people get their water from private wells in their leisure homes, out of a total population of around 10 million. The water from private wells can differ significantly in quality and composition. The treatment of water from private wells can include various steps, and in many cases filters and a microbiological barrier such as UV is used.   

The quality of the water at your tap will differ depending on the quality of the raw water and the primary treatment, however, in many developed countries it is normally safe to consume. 

What impacts the quality and safety of my water? 

Primary treatment

Like any engineered system, water treatment process at your water works or following your private well is designed based upon certain parameters, such as raw water composition and flowrate. Should these parameters change, the treatment of the water may be impaired. This is what happened in Östersund, Sweden, in 2010 as the raw water was contaminated by Cryptosporidium infecting 27000 inhabitants. 

Climate change is expected to increase the occurrence of extreme weather conditions such as heavy rains and floods. Both of these may impact the level of contaminants in the water as well as the flowrate.  


One of the greatest risks in the distribution system is ingress of contaminants from outside. In many European countries parts of the distribution network origins from the beginning of the 20th century. 

The distribution network contains a biofilm. Recent research from Lund University (co-authored by Catherine Paul and Kenneth Persson) show that “good” bacteria in the biofilm actually may continue to treat the water throughout the distribution system. 

As a consequence of climate change, increased floods and heavy rains may lead to increased pressure on the pipes with ingress of bacteria as a consequence, and even minor changes in ground temperature may lead to unfavorable changes in the biofilm. Organic matter is likely to accompany contaminants into the pipework, and a potential chlorine residual will react with the organic matter rather than the contaminants.   

Normal maintenance of the pipes also increases the risk of a temporary increase of contaminants in the water distribution system.  

Storage and consumption

Bacteria multiplies in stagnant water. This includes water tanks in RVs, caravans, boats, yachts, trains etc. Stagnant water may also occur in buildings, for instance following refurbishment impacting the premise plumbing leading to stagnant water in dead-end pipes, or if the building is not used.

Legionella bacteria is commonly found in water, and it thrives at temperatures between 20°-45°C. Legionella is not harmful to drink but can cause pneumonia or Pontiac fever if inhaled, for instance through aerosols in a shower.    

When would I benefit from treating my water?

In many parts of the world the primary treatment is simply insufficient. Or if you get your water from your own well it is also recommended to add water treatment. 

People with a weakened immune system have a higher risk of experiencing infections and severe symptoms. If you are in that category or are responsible for an establishment or institution frequented by people which may be in that category, such as a hotel, elderly care homes, cruise ships, and of course healthcare facilities, you should evaluate the risks associated to microbiological growth and temporarily elevated levels of bacteria and virus. 

If you are a business owner, adding water treatment could act as a differentiator, or to stay competitive. As a manufacturer of water dispensers, boats, RVs, showers, or residential water treatment equipment, or if you are a distributor of said products, or restaurant or hotel owner, adding or improving your water treatment is worth considering.  

If your water has a chlorine residual it may well be desirable to remove the chlorine taste. Similarly, your water could contain high amounts of minerals such as iron, manganese or high hardness which may discolor your porcelain or shorten the lifespan of plumbing or appliances.  You may choose to ensure that your water is free from bacteria and viruses for the same reason you wear a seat belt. Seat belts, as well as air bags, used to be an option when purchasing a car. Today they are both included as a standard item in all cars even though nobody expects to ever be in a crash, which is when you would need them.