Nobody seems to be mentioning that just drinking water is not going to do the job, at least not optimally. Pure water is hypotonic and will increase dehydration. Processing all that water pulls out electrolytes from the fluid in the body promoting electrolyte imbalance. Electrolyte imbalance is an issue anyway due to the tendency to lose electrolytes as water is lost, pulling the electrolytes out with it. All that pure water . . . hypotonic water . . . will itself promote chronic subclinical dehydration resulting in increased development of stones (kidney stones, gallbladder stones, salivary gland stones), as well as, importantly, significantly increased incidence of kidney disease. If you are drinking pure water only as opposed to water with electrolytes added, it is a crapshoot if you are going to get enough electrolytes from your food alone. Excessive loss of salt is a common problem, for example. There are others.
It is useful to understand that there is a sugar/salt relay in your small bowel with prompts it to uptake water (which is otherwise not its job). DripDrop is a good brand, there are multiple others. Be careful; Gatorade, for instance, has way too much sugar, and sugar at higher levels will itself promote fluid and electrolyte loss. Sugar, alcohol, caffeine, all three promote fluid loss, and with fluid loss there is corresponding electrolyte loss; best to address that as an issue when specifically using these.
Maintaining hydration is a subtly different task than rehydrating when you have allowed your body fluids to become depleted. Also, at levels that are too low, self rehydration does not work and a trip to the ER is required for intravenous rehydration. No colon means mental attention is required; the process no longer takes place automatically the way it did before. The small bowel does adapt over time to pick up some of the slack in water absorption/electrolyte regulation, but it isn't ever going to be the same as it is for a person with their colon, whose job it is in part to regulate water and electrolyte balance. It takes on average six to twelve months for most of the adaptation to take place, or so I read.
I use a combination of DripDrop single servings on an as-needed basis plus Berg or 1000 Keto (on Amazon) to keep magnesium and potassium in my water. I drink about 8-10 cups of fluid a day, which is enough for me, no colon and 5'8/135 lbs. I personally don't need to supplement much with salt, which is often wasted without a colon, but do tend to waste potassium, which other people seem to need less of, just my general impression. Bodies are individual and mileage varies.
I don't know if it will help anybody, but after my illness and surgery, imaging showed developing gallbladder stones. Once I was home, I started to add a serving a day in my water of something called CleanseDrops by Rejuvica, "kidney, gallbladder and liver cleanse" . . . the stones have disappeared entirely. I plan on continuing to do it daily for general health maintenance, trying to stay ahead of developing stones if I can, and to also, as best I can, avoid the consequences of long-term subclinical dehydration. Other people may have experience with this sort of approach; I'd love to hear them.
I am discussing the electrolyte issue here because I had to sort that out on my own; nobody made a whisper about it to me beyond the generic "drinks lots of water now" . . . so, in case there are any more "just drink lots of water" people out here, this is for you. I read that up to 47 percent of people with ileostomy surgery are rehospitalized within one month of surgery due to dehydration, and that twenty percent of people with ileostomies have acquired kidney disease within two years of surgery. It isn't a trivial issue. It also fortunately isn't that hard to manage water/electrolyte balance if you have the information you need, all things equal. Lots of variables can influence fluid retention; general guidelines are just general. Sickness, antibiotics, many medications, all can influence the small bowel's willingness to stand in for the colon.
Where to get information? You can search on YouTube for "ostomy dehydration" for videos, read the hydration material available on the major ostomy sites, and also I get a surprising amount of information from people who post reviews for the various ORS (oral rehydration solutions) available on Amazon, although many are of course just using it for hangovers or sports recovery. That is where, for instance, I found discussions on the WHO recommendations for oral rehydration solutions. I use about half the recommended amount for rehydration because I am maintaining hydration, not re-hydrating after losing ground. Your mileage may vary.
Maybe everybody already understands that drinking water has to be coupled with electrolytes to avoid the specter of chronic subclinical/clinical dehydration, but I didn't understand that myself when it was my turn, and nobody told me. Vague generalities and no clear, specific information about what I needed to do or how. I had to stumble down that path alone. So, again, just in case it might be of use to anybody . . . I have a glass (two cups) of electrolyte water (Berg or Keto1000, same formula) by my bedside at night. I drink some whenever I get up in the night, the water is usually gone by morning. When I do get up, I put a serving of DripDrop into two cups of water and chug it first thing. I have two more cups of fluid soon enough via decaf. Basically, I start my day with six cups under my belt without much trouble or focus. I keep electrolyte water at my desk and drink it as I feel like it. I don't really need to monitor . . . I am already six cups in when I start my day; I only need two to four more cups over the course of the day to meet basic body needs; I usually pick up the rest randomly in more electrolyte water, bone broth, coconut water (out walking around), vegetable juice, buttermilk, tea, whatever. Basically other than doing the DripDrop when I get up and preparing more electrolyte water when I run low, I really don't have to think about it at all. My blood tests for electrolyte levels and kidney function are excellent. And that's what I want . . . not to have to think about it much, bother with it much, and be ongoingly healthy regardless of whether I have my colon. Will I escape developing stones? I don't know. I'm doing my best but I imagine that is no guarantee. But I do imagine that trying to maintain appropriate hydration and electrolyte levels is the reasonable goal, and that can be approached at least. I'd love to hear how others manage the whole water/electrolyte maintenance task. I only know what I came up with on my own. Thanks!