Okay, so what you really have here, reminds me of some ultrasound I took a few mth. ago. I had some stomach pain, the doctor done some ultrasound photos, found nothing, but in the midst of those photo, they found something else that is minor but totally unrelated
Doing those blood test is normal pre-surgery. I personally don't prescribe to that theory because if the surgery needed to be done, then there is no choice 1 way or the other. If the surgery is not important, then sure, do the blood test is a wise precaution.
So in summary, you found a kidney issue that Pepper is drinking a lot of water. So let's assume that is really the case. But your vet also said there is 2 year to fix this.
So there are 2 things you can do:
1) w/ my rabbit specialist locally, the no. 1 diet for small animal supplement is this guy:
http://store.harrisonsbirdfoods.com/15-oz-ORGANIC-RED-PALM-FRUIT-OIL/productinfo/PFO/
The cost is inflated, don't buy it directly from him. But if you cut & paste the description of the text, and put it in the search engine, you'll find he's really selling this:
https://store.nutiva.com/products/organic-red-palm-oil
this is good for human and animals, only $6 for a big 32 oz jar. My vet has highly recommend this for my rabbits, and I have been giving this to my 2 buns and myself for years. Further, this product is certified to be Habitat Orangutan safe / friendly, meaning it didn't destroy any orangutan environment in the making of this product.
it's a very excellent product that should be given to rabbits w/ or without kidney problems
the idea behind this falls under the field of science called Nutrigenomics, (you are what you eat), in short, given proper diet, knowing you CANNOT alter your genes, you CAN alter the "Expression" of your genes.
The anti-oxidant inside will benefit Pepper. If you buy this, let me know, I'll give you more details on dosage and how to given this to human / animals, let me know
2) I have a few books on alternative medicine, I can upload to that acct. I told you, and eventhough they are meant for human, there are natural food that you can "wing" it for rabbits, for e.g., under Alternative treatment for kidney, from "Gale Group Encyclopedia of Alternative Medicine":
Supplementation with herbs that are blood cleansers
or blood purifiers is recommended. These herbs
strengthen the action of the liver and the kidneys, helping
with detoxification and excretion. Dandelion root
tincture (Taraxacum officinale) is recommended. Others
include burdock root (Arctium lappa), also known as
gobo, and can be purchased fresh at health food grocers
or in Asian markets. It can be used either raw or cooked
in salads, stir-fries, or other vegetable dishes. Burdock
root tincture can also be used. Red clover (Trifolium
pratense) makes a pleasant tea that can be consumed
throughout the day. Milk thistle seed (Silybum marianum)
can either be taken in tincture form or the seeds
can be ground up and eaten in combination with hot cereal,
granola, or other foods.
======================
If there is legitimate concern that you believe Pepper's kidney is in trouble, I would go to health food store, and see what kind of alternative preventive maintainence medicine is there for human on kidney, and try out a little bit for Pepper.
For e.g., using the above from Gale, you can get some Dandelion root, smashed it w/ a juicer, mix w/ some banana, and see if Pepper will eat it.
Let me know if you want to give this a go, if so, I can upload these ebooks tonight and you can download it, view these PDF, and search under the key word "kidney"
