What is the ruling on one who deliberately broke their fast during the day in Ramadan by drinking water in order to have intercourse with his wife, thinking that the expiation is fasting one day instead of fasting two consecutive months?

It is not permissible to break the fast in Ramadan without a legitimate excuse. Whoever intentionally breaks their fast by eating or drinking is sinful and must make up for the missed day and repent. Some scholars are of the opinion that expiation (kaffarah) is obligatory for one who intentionally breaks their fast, and this is the view of Malik and Abu Hanifa. Others hold that only making up the day and repenting are necessary. As for one who intentionally breaks their fast by drinking water in order to have intercourse with his wife, the correct view is that expiation is not waived for him. This is because his undertaking the sin of eating and drinking before intercourse does not warrant leniency, but rather calls for a more severe expiation.