**3.1 Food and Agriculture Organization (FAO), World Health Organization (WHO), and United States Environmental Protection Agency (USEPA) guidelines**

The guidelines for the safe use of reclaimed water in agricultural irrigation, according to FAO, WHO, and USEPA are discussed by Hacıfazlıoğlu et al. [50]; the guidelines comprise several parameters, such as electrical conductivity (EC), sodium absorption ratio (SAR), total dissolved solids (TDS), total nitrogen, total suspended solid (TSS), *NO*<sup>3</sup> − N , *PO*<sup>4</sup> −P , PAR, *HCO*<sup>3</sup> , boron, chloride, sodium, free chloride, *pH* , and turbidity. These parameters were classified according to the degree of restrictions: none, slight–moderate, and severe. For example, reused water having EC values <0.7 mS/cm is considered to not have any harmful effects on the ecosystem, whereas EC values >3 mS/cm will cause severe effects. Additionally, there is a high correlation between the SAR values and EC, based on the three classes of restriction on soil permeability (none, slight–moderate, and severe) [50].

### **3.2 Food and drug administration (FDA) guidelines**

The regulations set by the United States FDA as part of the Food Safety Modernization Act (FSMA) for water quality metrics were discussed by Rock et al. [51]. *Treatment Technologies and Guidelines Set for Water Reuse DOI: http://dx.doi.org/10.5772/intechopen.109928*

The regulations set by the FSMA are applied to the crops that are subject to raw agricultural commodities and do not receive commercial processing required to decrease the growth of microorganisms (to ensure public health). The FSMA has set standard processes, practices, and procedures that reduce the risk of serious health consequences or biological hazards in fresh raw crops (e.g., edible leafy greens) to decrease foodborne diseases resulting from the consumption of contaminated crops [51]. According to the Produce Safety Rule, farmers establish a microbial water quality profile (MWQP) for irrigation water sources (e.g., untreated surface and ground water) and are requested to perform annual surveys that can be used in the following years. The levels of generic *E. coli* are considered a basic parameter for the water quality profile in agricultural (pre-harvest) water. First, the MWQP must be performed, with not less than 20 water samples collected as near to the harvest period as possible, over not less than 2 years and not more than 4 and 5 years for surface water and ground water, respectively. The geometric mean (GM) or statistical threshold value (STV) is to be calculated from the collected samples using a minimum of five samples. The MWQP comprises both GM (126 CFU/100 mL) and STV (410 CFU/100 mL). The GM is an average that reflects the central tendency of the water source, whereas the STV represents the variations in water quality. Further details about the FDA FSMA regulations are presented in the literature [51].

#### **3.3 State-level guidelines in the United States**

In the United States, there are no established federal regulations for reusing recycled water. However, several individual states and territories (e.g., Arizona, California, Colorado, Florida, Virginia, Delaware, Massachusetts, New Jersey, Hawaii, North Carolina, Idaho, Minnesota, and Washington) have established specific regulations to manage reclaimed water for various purposes, including agricultural irrigation, animal watering, and crop production. Details about these state-level regulations are presented in the literature [51]. Notably, the regulations established by state standards for irrigation purposes to promote the use of recycled water to grow food crops are considered restrictive compared to the FSMA Agricultural Water metrics. This is indicated by the higher permitted concentrations of *E. coli*, total coliform, or fecal coliform bacteria, which are comparatively lower than those detailed in the FSMA metrics [51].

#### **3.4 Europe (Spain, Italy, Greece, and Cyprus) guidelines**

A comparison of guidelines for wastewater reuse in irrigational applications in Europe (Greece, Italy, Spain, and Cyprus) and the United States are discussed by Otter et al. [16]. These guidelines contain uncommon parameters for water quality, prescribing a limit for the number of pathogen indicators, to represent the effectiveness of the wastewater treatment plants in removing the nutrients, organic matter, and pathogens. Accordingly, the disinfection approach (e.g., ultraviolet [UV] radiation, membrane filtration, onsite chlorine generation system, and ozonation) is also a mandatory step to minimize public health risks resulting from potential exposure to reclaimed water [16]. In May 2020, a new regulation was proposed by European Union (EU) regarding the minimum quality requirements (MQR) for reclaimed water (EU, 2020/741) to be reused in the agriculture sector; this regulation will be implemented on June 26, 2023, in all the member states. There is also a growing concern about potential noncompliance situations regarding the MQR [52].
