Ruling on using Zamzam water to wash with after relieving oneself
Question

                Is it permissible to wash with Zamzam water after relieving oneself (istinja’)?
Praise be to Allah.
    The saheeh ahaadeeth indicate that the water of Zamzam is 
    blessed. It was reported in Saheeh Muslim (2473) that the Prophet 
     (peace and blessings of Allaah be upon him) said concerning Zamzam: “It 
    is blessed and it is food that nourishes.” A report narrated by Abu Dawood 
    [i.e., al-Tayaalisi] (1/364) with a jayyid isnaad adds: “and healing for 
    sickness.” This saheeh hadeeth points to the virtue of Zamzam water, stating 
    that it is food that nourishes and a healing for sickness, and that it is 
    blessed. The Sunnah is to drink from it as the Prophet  (peace and 
    blessings of Allaah be upon him) did, and it is permissible to do wudoo’ and 
    istinjaa’ with it, and to do ghusl for janaabah (impurity following sexual 
    activity) if that is necessary. 

    It was reported that water sprang from between the fingers of 
    the Prophet  (peace and blessings of Allaah be upon him), then the 
    people took it and used it for their needs; they drank it, did wudoo’, 
    washed their clothes and washed after relieving themselves. All of that 
    happened. Zamzam water is not like the water that sprang from between the 
    fingers of the Prophet  (peace and blessings of Allaah be upon him), for 
    there can be nothing superior to that, but both are blessed. So if the water 
    that sprang from between the fingers of the Prophet  (peace and 
    blessings of Allaah be upon him) could be used for wudoo’, ghusl, istinja’ 
    and washing clothes, then it is also permissible to use Zamzam water in 
    these ways. Whatever the case, it is pure and good water which it is 
    mustahabb to drink, and there is nothing wrong with using it for wudoo’, for 
    washing clothes and for washing after relieving oneself, if that is 
    necessary, as stated above. It was narrated that the Prophet (peace and 
    blessings of Allaah be upon him) said: “The water of Zamzam is for the 
    purpose for which it is drunk.” (Narrated by Ibn Maajah, 3062 – there is 
    some weakness in its isnaad but it is supported by the saheeh hadeeth quoted 
    above). Praise be to Allaah.