###### Abstract  
One of the goals of adding adjuvants to agricultural spray solutions is to enhance the droplet size characteristics of this spray. Droplet size, in turn, has an influence in the deposited spray quality, in addition to the drift and losses of spray to off-target places. The aim of this research was to evaluate the effect of adding adjuvants to two types of water from different sources on the droplet size characteristics. Two types of adjuvants were employed in the tests: the active substance content of the first adjuvant was a 50% aqueous solution of sodium salt of alkylbenzenesulfonic acid--10% (HY), whereas the second was from rapeseed oil (natural origin)--85% (OL). Both adjuvants were tested in two concentrations: the first was with the concentration recommended by the manufacturer (100%), whereas the second concentration was 50% of the recommended dose. Two types of water from different sources were used in the tests: the first was from a village in the eastern part of Poland (WS), whereas the second was tap water from the city of Lublin, Poland (WUP). D\({}_{\
u 0,1}\), D\({}_{\
u 0,5}\), or volume median diameter (VMD), D\({}_{\
u 0,9}\), Sauter mean diameter (SMD), relative span (RS), and the droplet size distribution were measured and calculated as characteristics of the droplet size. Results showed that the source of water affected the influence of adding adjuvant to the spray solution. Water from the WS source with adjuvant resulted in a numerical decrease in the D\({}_{\
u 0,5}\) values in the percentage of droplet size range below 150 \(\upmu\)m, whereas water from the WUP source resulted in an increase in these values (except when adding the HY adjuvant at 50% concentration). Adjuvant concentration significantly (\(p<0.05\)) influenced the features of D\({}_{\
u 0,9}\), SMD, and RS. Adding the OL adjuvant type numerically decreased the percentage of droplet size below 150 \(\upmu\)m, and the D\({}_{\
u 0,5}\) values, but only when the WS water source was used. apricultural nozzles; pesticide application; volume median diameter; surface tension; droplet size distribution +
Footnote †: journal: _Sciences_  
0000-0001-9993-2227][PERSON]  
1,* *  
affecting the contact angle and surface free energy, which in turn control the leaf surface wettability [2]. Adding adjuvants to the spray solution reduces the droplet surface tension [3; 4; 5; 6; 7; 8], contact angle values [3; 6; 7] and pH values [3]. Adjuvant addition enhances spray deposition and electrical conductivity [4], and improves the control efficacy of pesticides [9]. Moreover, adding adjuvants results in a higher wetting surface area [5] and increases the density and viscosity of the spray solution [6]. The concentration of adjuvant within the spray solution affects different parameters. The researchers of [10], for example, state that the adjuvant concentration has important effects on the spray droplet. Accordingly, the surface tension decreases when the adjuvant concentration is increased, as affirmed in the work of [11]. In addition, they found that the conductivity and chargeability of the spray solution was enhanced as the adjuvant concentration increased (except for a \"water only\" treatment). In turn [12], suggests that using the appropriate adjuvant concentration would result in a better uniformity of spray coverage on both waxy and hairy leaf surfaces. They also indicated that increasing the adjuvant concentration improves the wetted area of droplets. A study by [13] notes that adjuvant concentration changes the dynamic evaporation of spray droplets; this outcome may depend on the adjuvant property. Fine droplets can be expected when the surface tension of the droplets is reduced due to using adjuvants [10]. The researchers of [7] report a 33.5% reduction in the droplet size (D\({}_{\text{v0.5}}\)) after adding adjuvant to the spray solution. Those of [14] also note that adding surfactant-based adjuvants to the spray solution results in a slight reduction in the droplet size.