|It will only spread in a pool if your swimming with the leaves :P. The thing you worry about once someone has it, is infection. The most you can get from someone else is what ever they are carrying that's blood borne from oozing sores or a post exposure infection. You can not spread poison ivy unless the oil is still on the skin of the infected person. For instance, your pet can go roll on the leaves and you can play with the pet and get the poison ivy rash by transfer of the oil from pet to person.
In most cases the chlorine in pool water will help sooth the itch and irritation and help clean the wound. Most likely it will also disinfect what ever is oozing off the affected person. Chlorine is added to pool water to kill any bacteria that may set up in the standing water, it works the same on a person's wound. Don't count on it 100 percent to keep others from catching an unrelated infection, pools usually mean close contact and that means body fluids can get exchanged.
Exposure to poison ivy may take 3 to 5 days before you know you contracted it. It depends on a number of factors including, the persons sensitivity, skin thickness (the palms or soles of the feet rarely get blistered due to skin thickness), and the amount of exposure. In some cases it depends on what plant you dealing with too, poison ivy, poison oak and poison sumac (not all sumac) all contain the offending oil but only poison ivy has it throughout the entire plant. You can decease your chances of blistering by washing up quickly after a known exposure. There are products that say they can help decrease the chance of a rash by using them to clean up areas of know exposure. I usually use soap that is designed for oil removal such as plain ole dish washing soap. Scrub hard and long multiple times and be sure to get in between the fingers.
Blisters and the rash can last from 10 to 14 days. Once you have contracted the blistering the only thing you can do is treat the symptoms and an infection. No point trying to over treat it with bleach or any other type of chemical. All you end up with is a chemical burn on top of your blistering. Instead focus on relief from symptoms by using hydro cortisone creams, calamine cream, oral and topical antihistamines such as benedryl, and oat meal baths (aveno?). Keep your finger nails trimmed (no scratching)and keep the wounds clean. In some cases a doctor may need to give steroids in order to decrease the inflammation. If you start blistering on a large part of your body, face, eyes, or experience swelling or a post rash infection get to the emergency room or a doctor for treatment right away.