Water is a vital and therefore indispensable resource, but it is also often a strange liquid in terms of its behavior. Using well-known examples, we will therefore build a bridge between water as a resource on the one hand and phenomena or anomalies that occur due to the special structure of the water molecule in the water system on the other, in order to be able to recognize complex relationships and options for action.
When I reported on "Material loss minimization in surface finishing - generalized results of many years of research funding" in the specialist journal Galvanotechnik [1], water naturally also played a major role. It is well known that water must meet certain quality criteria for the preparation of process solutions and for rinsing treated workpieces. The water requirement must be minimized through multi-stage rinsing technology and water circulation in order to reduce costs and reduce or even avoid the use of drinking water. But also to enable internal material cycles and environmentally friendly waste water treatment with material recovery through concentration. And with the option of not having to discharge wastewater into the sewage system or directly into the water. The principles developed using practical examples can largely be generalized. This means that, under certain conditions, they can be transferred to other sectors.
However, water means much more than this and represents a much larger dimension as an indispensable resource, but also in particular due to its special physico-chemical properties, which give rise to numerous phenomena.
Water is omnipresent. After all, we encounter it in great variety as sea, rain, spring, surface, reservoir, ground, fresh, raw, brine, brackish, drinking, mineral, process and waste water, but also as soil moisture, softened, desalinated, old, fossil, juvenile, supercooled, dry, heavy, critical and virtual water, as well as ice, steam, crystal water and as a cell fluid in biosystems. Some of these terms overlap. However, the diversity underlines the importance of water and can serve as a stimulus for more in-depth study, as only an exemplary approach is possible in this article. It is also significant that water occurs in nature in all state forms (gaseous, liquid, solid) at the same time and plays an important role in all spheres (hydro-, geo-, atmo- and biosphere).
Water is life
This is demonstrated by photosynthesis, a material conversion process driven by solar energy for the formation of plant biomass and oxygen from carbon dioxide and water. There is no alternative to drinking water as food. Fluid deficits of just a few percent can trigger considerable dysfunctions in the human biosystem, including death. Due to the special structure of the water molecule, the physico-chemical properties of water are also very important for life and are the starting point for numerous water phenomena and anomalies. However, the effects of the special properties of water are often exaggerated and in many cases marketed in a questionable manner. More on this in detail and with examples in the course of the article. A critical commentary on the esoteric approach is provided from the perspective of a water chemist. Before that, a few remarks on water as a vital resource.
When talking about water in general and drinking water in particular, a quantitative and qualitative dimension must be taken into account. Quantitatively, water supplies and the distribution of water quantities within the natural water cycle play a decisive role when it comes to the availability of raw water for different forms of use, but especially for the production of drinking water. From a global perspective, the water reserves of around 1.4 billion km3 could give cause for optimism. However, the majority of this is salty seawater; only around 0.6% is freshwater, which forms the raw water supply for agriculture and livestock farming, industry and commerce as well as private households as groundwater and surface water. This small proportion is highly unevenly distributed globally and regionally, and this situation will become even more acute as a result of climate change and the associated changes to the natural water cycle. Regional extreme weather events, i.e. heavy rainfall with high water and flooding, and long periods of heat with water shortages due to heavy evaporation and groundwater lowering, illustrate this volume problem.
The water balance equation [2, 3] is used to balance water volumes in relation to a specific area and a specific time interval.
∆R = N - V - A<1>
∆R: Change in volume (storage/stockpiling)
N: Precipitation (mainland)
V: Evaporation (mainland)
A: Outflow to the sea (as groundwater and surface water)
In global terms, N=111, V=71 and A=40 (103 km3/a in each case) have applied to date. In connection with precipitation and evaporation over the world's oceans, significant changes are expected for N, V and A as a result of global warming, although these may have extremely different regional effects.
According to estimates by the World Water Council, around 3600 km3/a of A is temporarily diverted for human activities (70 % artificial irrigation in agriculture, 22 % industry, 8 % private households) [4]. Taking into account the approximately 7 billion people on earth, 3600 km3/a corresponds to an average per capita availability of freshwater of a good 500m3/a. According to the water shortage index, however, less than 500m3/a is already a water shortage. Reason enough to do everything possible to significantly increase the availability of fresh water.
There is an extreme water shortage in Kuwait, for example (per capita availability 10m3/a, U.A.E (61m3/a), Libya (107m3/a), Saudi Arabia (111 m3/a), Jordan (132m3/a) and others. Canada, on the other hand, is oversupplied with an availability of 93280m3/a, so that there is already talk of water exports. Overall, however, it can be stated that 1/4 of the world's population currently has to make do with less than 500m3/a[4].
Virtual water, which has to be allocated to industrial and agricultural products (e.g. approx. 15m3/kg beef), is also problematic in this context [25]. This results in additional risks for freshwater availability in many regions of the world, especially in water-scarce regions, and thus also for the supply of raw water for drinking water production. One example of this is the ongoing destruction of rainforest for the purpose of expanding agriculture, resulting in a significant reduction in groundwater levels, which in turn is exacerbated by the additional use of groundwater for the irrigation of ever-expanding agricultural areas. Water-intensive and export-oriented agricultural use in arid regions of the world is therefore ecologically senseless, but also economically unjustifiable. Arid regions should conserve their own water resources by importing water-intensive products.
It is worrying to learn that around 1.5 billion people already have no access to quality drinking water. The increase in conflicts over water as the basis of life is therefore inevitable if drastic countermeasures are not taken. Current example of conflict situations: The Blue Nile reservoir and hydropower plant in Ethiopia to secure energy supplies, but life-threatening water shortages in Sudan and Egypt. There is also potential for conflict between Jordan and Israel in the historic struggle over the extremely limited freshwater resources (Sea of Galilee, Jordan rivers, groundwater), which must be shared by mutual agreement - the outcome is uncertain [16]. Developed and territorially favorably situated countries, such as Israel, can partially compensate for water shortages through technical solutions, e.g. seawater desalination through reverse osmosis or other processes.
However, the fact that around 2.6 billion people have to live without basic sanitation is also extremely worrying. It is an indication that the scarcity of freshwater resources for human consumption is closely linked to the deterioration in water quality as a result of inappropriate use of water (e.g. pollution due to incorrect fertilization in agriculture, sanitation deficits, etc.). Population growth and densification play an important role here.
Germany has so far been considered relatively unproblematic in terms of its water resources and regional water distribution. In the ranking according to the Water Scarcity Index, Germany was on the safe side with an average per capita availability of freshwater of 2080m3/a(classification: adequate water supply) [4]. However, it is also becoming increasingly clear in Germany that extreme weather events are increasing as a result of climate change and are posing major challenges for raw water management, particularly with regard to a reliable drinking water supply in terms of quantity and quality.
One focus is groundwater, with a clear trend towards lower groundwater levels in some regions as a result of long periods of drought. Competition for use between water and agriculture is already evident. A critical point here is the intolerable increase in nitrate concentration in groundwater due to intensive agricultural fertilization [5, 25]. New regional concepts for securing the drinking water supply by using deeper, so-called fossil groundwater are being considered and will certainly be increasingly applied as climate change progresses. Cost increases for consumers are naturally to be expected.
The high surface tension of water enables capillary effects. This means that it can rise from the ground in the narrowest pipes of plants, here a lime tree in Upper Swabia
But drinking water reservoirs also react to changes in the climate. For example, research results from the Saxon Academy of Sciences in Leipzig have shown that phytoplankton growth (a measure of the degree of eutrophication of a body of water and therefore a quality criterion) is not nutrient-limited, but that the influence of temperature must be regarded as a significant growth factor [6]. When phosphate inputs were reduced by around 70 % after 1990, there should also have been a decline in phytoplankton growth (improvement in water quality), but this did not occur.
It is not only climate change that concerns raw water management, but also anthropogenic pollutant inputs into water bodies. Throughout Germany, it can be observed that a large number of known, but also as yet unknown problematic substances from agriculture, industry, contaminated sites, hospitals and private households can impair the quality of untreated water and thus pose a risk to drinking water quality. The trend is obviously rising. Examples of micropollutants that cannot or only insufficiently be eliminated in municipal sewage treatment plants are synthetic oestrogens and painkillers such as diclofenac and ibuprofen and many others. In general, this concerns all problematic substances with PMT properties (persistent, mobile, toxic) and their transformation products [5]. In total, there are said to be thousands of substances, many of which may well be relevant to drinking water. This is a difficult task for integrated water resource management right from the raw water quality assessment stage. The emphasis here is on "integrated". In addition to knowledge of complex substance structures, problematic individual substances, their origin, concentrations and transformations, their remobilization and distribution in water bodies, their elimination during raw water treatment to produce drinking water and the self-purification potential of aquatic ecosystems, it is particularly important to take measures to minimize the input of problematic substances into wastewater treatment plants and directly into water bodies. This could avoid cost-intensive additional investments in the areas of municipal wastewater treatment (4th purification stage) and water treatment. The surface finishing industries have already made a sustainable contribution in this respect with the research project mentioned under [1]. -to be continued-
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