Is it permissible to perform Tayammum for intercourse if there is not enough water except for drinking and cooking, while under siege?

If a Muslim cannot find water except for what is sufficient for his drink and food, or fears needing it in the future, he may perform tayammum (definition) to remove minor and major ritual impurity. This includes the need for water for drinking, preparing food, or removing impurity. When tayammum is permissible, it temporarily substitutes for ablution (wudu') and ritual bathing (ghusl (definition)) until water becomes available. It is permissible for a person in a state of major ritual impurity (junub) to engage in marital relations after performing tayammum.