This pot wasn't fired to store water or grain. Rather, it was commissioned during World War II by the Japanese colonial authorities to serve as a one-man air-raid shelter. Contemplating the possibility of Allied forces landing on Taiwan's beaches, the Japanese (who ruled Taiwan between 1895 and 1945) ordered hundreds of these pots, which could be buried in sand or soil, horizontally or vertically, protecting individual soldiers from bullets and bomb fragments.
According to information at Shuili Snake Kiln (水里蛇窯), where I took this photo, because Taiwanese potters were needed to produce these air-raid shelters and other items needed for the war effort, they were exempted from conscription into Japan's imperial armed forces. Similar pots were also bought by wealthy individuals; one is on display inside this traditional courtyard house.