King 800/6000 PB04 combo sharpening water stone for 20$ at https://www.amazon.com/dp/B008FU4332

Size: 7.3"(185 mm) x 2.5"(63 mm) x H. 1.0"(25 mm). Please put it into water for about 3 mins before you use and sharpen your knife or any other tool with enough water inside. No water needed for #6000 Fine. https://yuisenri.com/products/king-pb-04