The limitation of water resources and remarkable increase in population should force research workers to find ways for saving water without significant reduction in yield. So, two field experiments were  carried out  at Water Management Research Station, El-Karda and Irrigation Development Area at El-Wazaria, Kafrelsheikh, Egypt, during the two growing seasons of 2013/14 and 2014/15 to study the mutual effect of withholding irrigation and potassium fertilizer  on yield and water productivity of wheat. Split plot design with four replicates was used. The main plots were devoted to irrigation treatments while the subplots were assigned to potassium fertilizer. Irrigation treatments were  full irrigation (W₁) including tillering (T), Jointing (J) , booting (B), heading (H) and milking (M) stage, and it has been added to a 60 cm of the root zone depth; full irrigation (W₂) including T,J,B, H and M stages, and it has been added to a 40 cm of the root zone depth; withholding irrigation (W₃) at M stage;  withholding irrigation (W₄) at B stage; withholding (W₅) at J stage; withholding (W₆) at J and B stages and withholding (W₇) at J,B and M stages. All withholding irrigation treatments were irrigated to a 40 cm of the root zone depth. Potassium application treatments were 24 kg K₂O feddan as basil along with foliar spraying twice using 2 % of potassium sulphate at 35 and 55 days after sowing and control treatment without application. Results showed that insignificant increases between full irrigation treatments of W₁ and W₂ in spike No. m^-2, spike length, kernel No. spike^-1, 1000-kernel weight, grain weight spike^-1 , straw and grain yields in both seasons .No significant differences in the most of these traits were noticed among withholding irrigation treatments of W₃, W₄ and W₅ that received  four irrigation and W₁ especially in the first season that receive irrigation twice because of high rainfall. Seasonal water applied amounted 2517, 2025, 1815, 1722, 1758, 1456 and 1246 m³/fed. and water consumptive use values   were 1584, 1480, 1327, 1234,1270, 967 and 755 m³/fed. over the two seasons for W₁, W₂,W₃,W₄,W₅, W₆ and W₇, respectively. Withholding irrigation treatments of W₇ resulted in the highest water productivity to be 2.5 kg grain m^-3 over both season. Application K fertilizer (K1) significantly increased straw yield and grain yield and its components except spike length.  The interaction between irrigation treatments and K fertilizer had significant effect on the most studied traits in both seasons. Application of K fertilizer diminished the negative effects of withholding irrigation on yield and its components. Application of K fertilizer did not effect on seasonal irrigation water and consumptive use, but it increased water productivity through increasing grain yield. At North Delta, Penman Monteith equation can be used in determining the actual consumptive use and the average of crop Coefficient (Kc) for the two seasons  was found to be 0.87, 1.07, 1.11, 1.17, 1.23, 1.28 and 0.35  during emergence, tillering , jointing, heading, milking and ripening stages, respectively. Therefore, when water is becoming a limited factor for wheat production, it should applied withholding irrigation at J or M stages with potassium fertilizer to reduce the negative effect of withholding irrigation at some growth stages and to keep the productivity without significant reduction.