The difference is that it used to be necessary to change the water for Alizu on the 1st and 15th of every lunar month, whereas now that has been simplified to twice a year--on the spirit's birthday, and at Ghost Festival.
「就看伊們怎麼拜，阮就怎麼拜。」不過本來應該初一、十五為阿立祖換水，現在卻簡化成一年兩次（生日和中元）啦！