One of the regional consequences of climate change is that weather extremes are becoming more frequent [1], so our water management needs to be reconsidered. The main problem in itself is not that the annual amount of precipitation decreases, but that the precipitation does not arrive evenly [2] and summer drought periods become more frequent [3]. Climate change and the consequent increasing dryness, forest fires, the lowering of the ground water level and the beginning of soil erosion all contribute to the process of desertification, but many factors directly related to humans are also to blame [4]. Industry and agriculture are primarily responsible for water consumption. The latter accounts for about half of the total water consumption [5]. To the best of our ability, we must do everything we can to prevent and reduce the damage caused by drought, so that we can supply water at the right time and in the right amount. Water supply plays a key role in the conditions for competitive agriculture, and the efficient use of irrigation water of adequate quality can be a key element of this supply.

One of the biggest challenges of the 21st century is determining how to provide enough clean water for everyone (agriculture, industry and the entire living world) and not just the population [6]. Irrigation is the artificial application of water to the surface of the soil and then to deeper layers, using a variety of specialized equipment (e.g., pipes, pumps and sprinkler, dripping systems). Irregular rainfall distribution and drought make irrigation necessary in certain areas. A wide range of irrigation systems are available to distribute water evenly over the surface to be irrigated. The water used for irrigation may originate from ground water, spring water, well water, surface water, rivers, lakes, reservoirs, or even treated wastewater or desalinated water [7]. The use of irrigation and targeted nutrient supply in quality and intensive vegetable and fruit cultivation has been spreading more and more in recent years [8]. The quality of the crops, their aesthetic appearance and the life of the irrigation system are both influenced by the quality of the water used for irrigation [9]. There are many options available for irrigation water treatment. Biological treatment methods could be promising for organic and heavy metal compounds; however, they require precise operation and control. For salt removal, many studies have reported electromagnetic and electrostatic treatment as fast and quite easier treatment methods; however, the efficiency of these techniques could be lower since they are a pressure-driven membrane separation process. The use of adsorbents can be a good way to remove certain undesirable components of irrigation water. Two large groups of adsorbents are known: conventional and non-conventional adsorbents, which can achieve different efficiencies in water purification. Conventional adsorbents generally have a higher adsorption capacity compared to non-traditional adsorbents, which are readily available and therefore inexpensive, but have a lower adsorption capacity.

Nowadays, it is no longer enough to provide the physical conditions for irrigation; there are also an increasing number of legal requirements to be met. As environmental requirements are becoming more stringent due to the increasing value of clean water, no water-based activities can escape the scrutiny of the legal regulatory regime. In the following, the most important aspects and principles will be summarized; these may influence professional conclusions.

The regulatory background for irrigation covers a wide range of legislation, depending on the source, quality and agricultural area of the irrigation water.

In Hungary, the concept of water management and the related responsibilities serves to comply with the relevant EU and national legislation, i.e., it includes compliance with the requirements of Directive 91/271/EEC [10] on urban wastewater treatment, Directive 98/83/EC [11] on the quality of water intended for human consumption, the Water Framework Directive, Act LIII of 1995 [12] on the protection of the environment, Act LIII of 1996 [13] on the protection of nature, Act CLXXXV of 2012 [14] on waste, and Directive 2007/60/EC [15] on water damage.

The European Union Directive 2000/60/EC [16] is the most important and community-wide guideline for the protection of the good quality of the water bodies covered by the community.

The EU’s Water Framework Directive (WFD) aims to achieve and maintain the good status of surface, coastal, transitional and groundwater, thereby contributing to the protection of ecosystems. An important objective of the Directive is to prevent the pollution of waters, and it sets limits on anthropogenic emissions. The measures taken to achieve and maintain the objectives set out in the WFD are summarized in the river basin management plan at a national level.

Decree 90/2008 (18 July 2008) [17] of the Ministry of Agriculture and Rural Development stipulates that a soil protection plan must be drawn up for, inter alia, irrigation for agricultural purposes, on the basis of which the justification for the measure must be presented and a proposal for protection against erosion must be made after soil sampling in an accredited laboratory.

In response to the challenges of climate change, to improve the competitiveness and adaptability of agriculture, to promote the wider use of irrigated agriculture and to establish irrigation communities, the National Assembly has enacted Act CXIII of 2019 [19] on Irrigation Agriculture. According to the law, “In order to carry out irrigation farming, the holder of the water right of the water facility is entitled to an irrigation easement, under which the owner or user of the property served must tolerate the establishment and operation of a linear water facility for irrigation on his property by the farmer carrying out irrigation farming, to carry out the necessary water works for the purpose of irrigation for the continuation of his agricultural activity, and to transfer the irrigation equipment, provided that it does not preclude the proper use of the property”.

It can be seen from the above that the Government is seeking to promote the competitiveness of agriculture and the protection of land and water through the appropriate use and quality of the land, in accordance with the objectives of the European Union. More modern, but more expensive irrigation technologies, can achieve the more sustainable use of water. These aspects will become increasingly important in the future.

The most common sources of water available for cultivation are surface water (water from lakes, canals, possibly rivers) and underground water [20]. For subsurface waters, we must separate groundwater and aquifers from a quality point of view. Groundwater is the water of the first water-tight layer, and water bodies shallower than 20 m (dug and drilled wells). Aquifers are located in layers deeper than 20 m, depending on the geological and hydrological conditions. These waters may only be extracted with pre-planned and authorized wells. The professional basis for this is to protect it from possible pollution from the surface, since it is our most valuable, cleanest, long-term water reserve [21].

From the perspective of producers and water users, the quality assessment of the three types of water is quite different. The differences are to be found in the constancy of the composition and the effects of environmental pollutants. Surface waters are constantly exposed to quality-affecting influences: inflows, water withdrawals, precipitation, washing in, dilution, and concentration, which constantly modify the composition. When using surface water for horticulture, constant caution is a good idea; at the very least, we should measure the salinity (EC) on a weekly basis, which draws our attention to major changes. Regarding groundwater wells, we can say that their waters can only be recommended for horticultural crops with greater compromises, because they can contain not only a significant amount of nutrients, but also harmful substances accumulated to a toxic level [22].

The quality of irrigation water varies from country to country. For irrigation, natural water quality would be the most suitable; however, we cannot usually ensure rainwater quality from the available water sources. Therefore, in addition to the positive effects, irrigation can also have negative effects (Table 1), which are partly due to the water quality [23].

The quality of irrigation water refers to the range of properties of the water to be used that affect the soil, the life processes of the plant and the technology of water distribution. Therefore, when determining the quality indicators of irrigation water, it is advisable to examine the triple interaction of water–soil–plant [7,24]. Methods for ensuring water quality have developed continuously and basically set certain limit values based on two aspects, namely the effects on the soil–plant combination and the effects on the operation of irrigation equipment. The first group basically includes chemical parameters, and the second group includes physical, chemical and biological parameters [25].

Among the chemical requirements, the most important characteristics are as follows:

• salinity,
• indicators expressing the effect of hydrocarbons and carbonates,
• the amount of sodium ions compared to calcium–magnesium ions,
• the relative ratio of magnesium,
• electrical conductivity,
• chloride, iron and manganese content [26].

Changes in the pH of the water during cultivation will affect the quality of the plants. A low pH inhibits the absorption of vital nutrients such as calcium, potassium, magnesium and molybdenum [27]. At the same time, a low pH increases toxicity because some trace elements are absorbed too easily [28]. At too high a pH, other substances such as phosphates and other important trace elements become unavailable to the plant [29].

The sodium adsorption ratio (SAR) is the most important characteristic. It means a value representing the relative amount of sodium ions to the combined amount of calcium and magnesium ions in water using the following formula: SAR = [Na]/(([Ca] + [Mg])/2)^1/2, where all concentrations are expressed as milliequivalents of charge per liter [30]. Salinity is generally dangerous for the soil, but it can also be harmful to plants. Salinity is expressed by the amount of salt dissolved in a volume unit (g/L) or by the specific electrical conductivity (EC) of the solution. When establishing the limit values, the primary consideration is that the irrigation water should not cause a level of salt accumulation in the soil that could be harmful. Therefore, it is not possible to establish a general rule regarding this, because it depends on many properties (e.g., water permeability, rainfall, irrigation method, salt tolerance of the plant [31]. It is generally accepted that if the salt content of the irrigation water is less than 500 mg/L (EC < 0.78 mS/cm), then the salt pool of the irrigated soil usually does not increase significantly [32].

As a result of certain environmental changes (e.g., concentration, dilution, increase in pH), some of the Ca and Mg ions precipitate out of waters with a high carbonate–hydrocarbonate content [33], thus increasing the proportion of Na ions in the solution, and thereby making the water salinizing [31].

Various parameters have been proposed to estimate the amount of carbonate and hydrocarbonate ions and their expected chemical interactions, e.g., phenolphthalein alkalinity, soda equivalent, saturation index, effective Ca and Mg concentration, relative hydrocarbonate and carbonate ratio [34,35]. The principle of certification in this area is that high-quality irrigation water must not contain free soda at all and must not show phenolphthalein alkalinity [36].

In terms of the cation composition of the irrigation water, a low sodium level is favorable [37]. However, in terms of the salinizing effect of water, the most important thing is not the absolute amount of Na-ions, but their proportion compared to other cations [38]. Sodium is a natural component and enters the water through the dissolution of minerals, but it can also be of municipal origin. It is the biggest problem in soil cultivation, where it has a harmful soil-destroying and salinizing effect; this is because it replaces other cations (e.g., calcium ion) on soil colloids and thus significantly changes the structure, functioning, nutrient and water management characteristics of the soil [39].

A significant amount of magnesium ions from irrigation water with a high magnesium content can bind to soil colloids, which adversely affects the physical and water management properties of the soil. Therefore, it is advisable to take the Mg/(Ca + Mg) ratio or its percentage into account when classifying water [34,40].