What is the ruling on tayammum for a people suffering from water scarcity and intense heat in shelters?

It is not permissible to perform tayammum (definition) (dry ablution) when water is available, except in the case of illness where the use of water would be harmful, or if there is insufficient water for purification and essential needs (drinking and cooking). Therefore, anyone who has water in excess of their essential needs and is not ill must purify themselves for prayer (ghusl (definition) or wudu). If one performs tayammum in this situation, their prayer is invalid, by agreement of the scholars.