The reason this is a bad idea for IC patients, as some of us have learned, is that the less water you drink, the more concentrated your urine becomes. If your urine is very concentrated it will cause an increase in your pain which can lead to still having the sensation that you have to "go" but because you don't have a sufficient amount of urine for your bladder to expel, we end up trying to force out these small amounts. That's not good because doing that can just make matters worse by contributing to pelvic floor dysfunction. If you are drinking the right amount of water, your urine will be more dilute and thus reduce the level of pain when you do have urine in your bladder and your bladder will have enough urine in it to function properly and allow you to void naturally without trying to force it out. It can also aid in flushing out anything you may have consumed that is irritating your bladder.
For the majority of IC patients, you do not need to drink gallons of water but you do need to be drinking it throughout the day. The surefire way to tell if you are taking in enough water is if your urine is clear or nearly clear (pale yellow). If it looks dark or very gold, you are not getting enough fluids and should increase your intake.
So how much is enough? You do not need to drink gallons of water (I'm not talking about patients with other issues like kidney problems who may need more than a patient with IC). But you do need to be drinking throughout the day. Buy a refillable water bottle (mine holds 24 oz. of water) and sip from it all day long. I usually drink my entire bottle by late afternoon and refill it but never finish it after it's been refilled. This seems to be just the right amount for me. For some of us who never drank enough water before we got IC, this can be an effort to re-train ourselves. It was for me. I was a Diet Coke "addict" and when I was diagnosed with IC I knew I had to give that up and start drinking water. That was a challenge for me. I didn't quit "cold turkey" but did it gradually and by doing so, I never suffered caffeine withdrawal. I got a water bottle and began working to drink my water. In the beginning I was drinking way more than was necessary and that wasn't good either. It took talking to my doctor and playing around with the amount before I figured out the right amount for me. It's worth the work if you've not been a water drinker. It's healthier for you anyway, and it definitely helps with your IC.
If you are experiencing this extreme heat as we are here in Illinois, then it may be appropriate to increase your water intake, especially if you are able to exercise outside or are just spending time outdoors. Even healthy people are instructed to stay hydrated in this heat. It's even more important for IC patients. A key that medical professionals use when reminding people to stay well hydrated if you are outdoors in this extreme heat is, if you wait to drink until you are thirsty, it's too late. So if you are still able to exercise, and are doing so outside in this heat, make sure you are taking water with you and drinking it before you feel thirsty!
The point is, obviously to say well hydrated. It's just good health regardless. But get used to carrying a water bottle with you; I take mine everywhere I go most of the time (it's at least in my car if I don't want to carry into wherever I may be going). If there are other beverages you can drink that don't bother your bladder, those can count toward your fluid intake. If there are a few rare IC patients that can still drink beverages with caffeine, those won't count because caffeine is dehydrating, so you must compensate and not count those as part of your fluid intake. Most IC patients have had to give up anything with caffeine so this isn't a consideration, but just in case we have a few rare individuals who can still drink a little caffeine, remember to keep your water bottle with you and sip from it throughout the day.
I just wanted to touch on a subject that may be something new IC patients need a little help with. If you'e an old hand at this, you probably already know this. But it never hurts to remind us of some of the small things that can be so important in our self-care and doing all we can to help ourselves manage our IC symptoms.
So get used to it; water is an important part of your IC life! Drink up! You'll be glad you did!