Is it forbidden to pour water in which flour has been dissolved into the drains?

There is no harm in discarding flour that cannot be utilized. However, if it can be utilized, then it is not permissible to discard it, as that would entail wasting God's blessing, extravagance, and ingratitude. Allah Almighty said: "Eat from the provision of your Lord and be grateful to Him." If it is possible to feed it to poultry, that is preferable. If it must be discarded and cannot be utilized, then it is better to discard it in clean places.