Phosphate in drinking water

Basically, we in Germany are blessed with good and above all drinkable tap water. Some drinking water reservoirs offer the perfect chemical composition so that deposits of lime and corrosion in the pipelines do not stand a chance. However, this is rather rare.

Among other things, phosphate is present in drinking water. But what exactly is the purpose of phosphate in water? How does phosphate affect our health? Which limit values are decisive for humans and the environment? About all this and more we clarify in this article.

What exactly is phosphate?

Phosphates are salts and esters of phosphoric acid. Since phosphorus is a very reactive element of the nitrogen group, the chemical substance forms countless compounds. This is also the case in our body: phosphates, together with sugars and bases such as adenine, guanine, thymine and cytosine, are an integral part of human DNA.

The term phosphorus is derived from the ancient Greek word “phosphoros”, which means “light-bearing”. Phosphorus has the property of glowing in the dark, which is the reason for its name. Phosphorus is the name for any organic and inorganic nitrogen compounds, whereas phosphates are compounds of the element phosphorus with oxygen.

The element phosphorus can react with both bases and acids and can only be found in nature in bound form. There it is contained mainly in minerals such as apatite, phosphorite and igneous rocks. In order to use the element, it must first be mined and split off. However, since phosphorus is an excretory product, it always ends up back in nature’s cycle in a natural way. Thus, every person excretes a quantity of about 4.5 g of phosphate every day.

In chemistry, a distinction is made between primary, secondary and tertiary phosphates . For example, hydrogen and dihydrogen phosphates are formed by the neutralization of phosphoric acid.

The industry has taken advantage of phosphorus. Phosphates are mainly used in agriculture as an additive in fertilizers or in food and feed as an additional nutrient. Furthermore, phosphate was added to detergents as a softener for a long time, which has been banned in Germany as well as in Switzerland since 1986 due to the increased phosphate content in groundwater. Phosphates are also found in corrosion inhibitors, which means that they can also be found in our drinking water.

How does phosphate get into drinking water?

In natural waters, phosphorus occurs only in small amounts. High concentrations are mainly due to the excessive use of phosphate-containing fertilizer in agriculture. Years of careless phosphate additions have had a major negative impact on the water and the environment. For example, increased phosphate levels in water bodies led to increased blue-green algae growth, which is one of the reasons why many animals and plants are endangered. However, according to measurements in Hesse, a high value of phosphorus in natural waters is mainly due to sewage treatment plants.

Through irrigation and leaching of the soil, the phosphates eventually also reach the groundwater. Therefore, rural areas with a high agricultural economy often have higher phosphate concentrations in tap water than other areas.

Similarly, the Lower Saxony Chamber of Agriculture believes that soil erosion also has a high impact on phosphates in drinking water. For example, anemic bogs, peat soils or soils with a high humus content are said to increase the phosphate content in groundwater and thus also in our tap water.

In addition, the drinking water can be deliberately enriched with phosphates to prevent deposits, deposits or the formation of limescale.

Is there a limit value for phosphate in drinking water?

In order to contain or keep under control the phosphate concentration in drinking water, the German Drinking Water Ordinance set a limit of 6.7 mg per liter in 1990. At that time, exceedances were only allowed for drinking water from wells or in areas with a lot of agriculture. However, surface water near certain industrial facilities could also have elevated phosphate levels.

However, the current version of the Drinking Water Ordinance since 2001 does not specify a limit value for phosphates in drinking water today.

Who is responsible for phosphate in drinking water?

In principle, water quality monitoring is the responsibility of the waterworks.

However, private homeowners are also required to regularly check and monitor drinking water. For example, they must take independent action if an unfavorable pH or hazardous pollutants are detected during a water quality check.

However, since the Drinking Water Ordinance no longer prescribes a specific limit value for the content of phosphate in drinking water, both private households and the responsible waterworks cannot react appropriately in the event of an increased phosphate concentration.

In addition, compliance with the levels of other pollutants is also proving difficult. The German Drinking Water Ordinance specifies only 50 pollutants with corresponding limit values, although drinking water can contain around 100,000 pollutants.

In addition, different areas of Germany may also have different types and concentrations of pollutants due to the composition of the soil, varying degrees of soil contamination, and differences in purification performance, which is also not regulated by the requirements of the Drinking Water Ordinance.

Have phosphate content tested

As a rule, it should be assumed that tap water is of carefully tested quality and that the municipal utilities take care of the testing so that we receive clean and safe drinking water from our pipes.

Nevertheless, an independent check of the phosphate content in the drinking water is worthwhile. In addition, heavy metals, minerals and bacteria can also affect the quality of tap water or attack the pipe system. For example, a laboratory sample of the water can provide information about the pH value, contained nitrogen compounds such as nitrate, nitrite and ammonium, as well as conductivity and the degree of hardness. After discussing the causes, a water quality test can help ensure that appropriate action is taken early and that both health and plumbing are spared.

Can phosphate in drinking water have health consequences?

A certain amount of phosphorus is essential for human life. Therefore, the phosphate contained in drinking water usually has no negative impact on health.

Phosphorus is needed, among other things, for the formation of adenosine triphosphate (ATP) in the body. This chemical molecule is needed by both animals and humans to provide energy. In addition, phosphate contributes to a healthy structure of bones and teeth. Therefore, an adult needs about 800 mg of phosphorus per day. A deficiency can lead to weight loss, weakness and fatigue, among other things.

However, due to the high concentrations of phosphate in our food and drinking water, a deficiency is unlikely and very rare. On the contrary – most people consume more phosphorus than they actually need.

Nevertheless, for a healthy person, there is usually no health risk from the phosphate in tap water, as long as excessive amounts of foods with high phosphate content such as cola, processed cheese or sausages are not consumed. Otherwise, one must reckon with long-term consequences that affect, for example, heart health, blood vessels, blood circulation or bone strength.

People with conditions such as chronic renal insufficiency or hyperthyroidism should also avoid excessive phosphate intake, as should infants, toddlers, children and adolescents.

However, some phosphorus compounds can be quite life-threatening. And this is when the composition has a dangerous effect on the human organism. White phosphorus is thus lethal at 50 mg, but death occurs after five to ten days.

What can be done about phosphate in tap water?

A low phosphate load of already 0.3 mg/l in the water can be an indicator for fecal pollution. Fertilizers, a high wastewater load or deliberately added phosphate-containing protective agents against corrosion can also be among the causes of increased levels of phosphate in water. Because high levels of calcium and magnesium carbonate can cause limescale, water utilities are often required to add phosphate-based corrosion inhibitors. The addition of phosphate reduces water hardness and solves the problem of unwanted or harmful deposits in the pipe system.

Nevertheless, as a private homeowner, you can consider water treatment to obtain demineralized water, for example. This way, you have flawless drinking water available, which is not excessively contaminated with minerals and pollutants and can also prevent limescale deposits.

Reverse osmosis

A good way to obtain phosphate-free water is the purification process of reverse osmosis as part of water treatment.

In an osmosis process, technical means are used to create a pressure between two liquids with different concentrations of dissolved substances. The so-called osmotic forces occur when these two liquids are located at a semipermeable membrane. The pressure is created by both fluids trying to equalize the concentration of solutes.

Since the membrane is permeable on one side, either the liquid with the higher concentration will flow in to the side with the lower concentration so that both reach the same concentration. Or it is intentional that the liquid with the lower concentration dilutes the other. This process allows the pressure to develop.

However, with reverse osmosis, concentration equilibrium is not the goal. Therefore, a counterpressure of up to 30 bar is applied with the help of a pump. The concentration gradient is therefore not decreasing, but increasing. In this way it can be achieved that the liquid – in this case the water – is purified from all substances contained in it. The solution on the other side of the membrane is now highly concentrated and must be disposed of, which in turn creates a lot of wastewater.

The water produced by this process is also called osmosis water . The quality of osmosis water is almost as pure as distilled water. It is also very soft water, which has a hardness level of zero, because reverse osmosis removes all calcium and magnesium ions. As a result, limescale cannot form and the pipelines always remain free of deposits. Phosphate is also removed from the water.

For drinking water treatment in private households, such reverse osmosis systems are usually offered as central systems. However, these are very expensive and, in addition, water purification is very energy-intensive, which should also be taken into account.