Any leftover donations can be used for any permissible, religious, reformatory, welfare, spiritual, benevolent and good purpose.
Water
Well
Hadrat Sayyidunā Sa’d bin ‘Ubadah رضی اللہ عنہ asked, “Ya Rasūlullah َصَّلى اللُه َتَعاَلى َعَلْيِه وآلہ وسلم ! My mother has passed away (I want to give some Şadaqah (charity) on behalf of her), which Şadaqah would be the best for her?” The Holy Prophet صَّلى اللُه َتَعاَلى َعَلْيِه وآلہ وسلم replied, ‘Water.’ So, Sayyiduna Sa’d رضى الله عنه got a well dug and said, “This is for Sa’d’s mother.” (Sunan Abū Davod Sharif, V2, P53, Hadis 1681, Dar-ul-Fikr Beirut)