Pure solid IPTG does not smell, suggesting that your sample has degraded releasing a mercaptan (the human nose is sensitive to thiols). A paper describing the pharmacology of IPTG suggests that it is stable in mice (Nucleic Acids Res. 1991 Sep 11;19(17):4647-53.) if that helps. For in vivo studies I would use saline rather than water for your experiments.

Dear Alan,

Thanks for your comment. We are also thinking that the compound degraded. When we inject IP we indeed use saline but as a stupid question will the mice drink saline?

Not through choice. Sometimes sucrose can help encourage drinking if a compound is present with an unpleasant taste. Fluid intake is higher ai night when the mice are more active and if more regular fluid intake is required, then switching them to a 12 hour day / night cycle can help.