It's still remarkably tone deaf, regardless of the actual percentage of the reservoir being used up per bucket. At least, for those Challengers doing it in Cali it is.
Comparatively tone deaf: George W. Bush doing the IBC the other day. You know, since he's not exactly a man with a healthy history when it comes to water being dumped on people's heads.
If you can understand the objection to the latter, you can understand the objection to the former. Whether it's for a good cause or not.