... this demand is politically stupid.
Read the letter.
It should be obvious from the last few election cycles that America is nowhere close to accepting such a demand. Making it will just inflame those on the right and make you look stupid or overly-demanding to those in the middle. This hurts your credibility and makes it that much harder when you need to ask the government for something else in the future.
A better/more-politically-savvy approach would be to issue a softer, open-to-negotiation request/suggestion/demand that new large-scale electricity-consuming sites only be approved if they provide for the production and delivery of electricity without causing significant additional harm to the environment. This approach might ultimately fail to get what you are asking, but at least it wouldn't come across as a whiney demand from someone who thinks they are entitled to getting their way.
For what its worth, this weaker, more reasonable demand would still shut down some planned projects and anger some investors, but it would allow it if the planned project could either
* Build an on-site environmentally-sustainable power plant,
* Buy electricity from an existing source, but only if it wouldn't strain the grid's production or delivery capacity (this option is likely the most feasible as long as the project is powered down during peak hours)
* Buy electricity from an existing source and pay to have additional transmission lines run so it doesn't hurt the existing transmission network,
* Pay to build a new environmentally-sustainable power plant, but only if the transmission grid can handle the load,
* Or some combination of the above.
As for water consumption, it's reasonable to ask that new facilities use either air cooling or closed-loop cooling, so there is no wasted water.