An adapter for connecting a water pipe and a high-pressure spray gun includes a connection assembly, a clamping assembly, and a covering member. The connection assembly includes a connector body defined by a side wall and extending between a proximal end and a distal end, and a chute that extends along the connection body between the proximal and distal ends. The water pipe is coupled along the proximal end and the spray gun is coupled along the distal end. The chute includes grooves, and tapered regions seamlessly extending below from the grooves. The clamping assembly is operatively coupled to the connector body. The covering member sleeves over the connection assembly to movably engage with the clamping assembly, and is pressed and released to realise the buckle to move down from the grooves towards the tapered regions and back from grooves to the tapered regions, to clamp the water pipe.