Does drinking water by mistake during the day in Ramadan count as intentionally breaking the fast, which necessitates expiation?

If a fasting person eats or drinks out of forgetfulness during the day in Ramadan (definition), their fast is valid, and there is no need for them to make up the day (qada') or offer expiation (kaffara). Therefore, your first breaking of the fast by drinking water out of forgetfulness does not invalidate your fast, and you should have continued fasting for the rest of that day. However, since you did break your fast and subsequently made up the day, there is no expiation required of you, as expiation is only obligatory for someone who deliberately breaks their fast by engaging in sexual intercourse during the day in Ramadan.