Which of the following is a way to use water economically? 

Drip irrigation 

The correct answer is option 3. Drip irrigation.

Drip irrigation is a way to use water economically.

Drip irrigation is an irrigation method that conserves water by delivering it directly to the base of plants through a network of tubes, pipes, valves, and emitters. This targeted approach minimizes water wastage by providing the right amount of water directly to the roots of plants, promoting efficient water use in agriculture and landscaping. Therefore, the correct option is Drip irrigation.