Because if you use real water it will burn your eyes and contacts wont.
The better alternative is no water pollution for clean drinking water
Take your contacts out right away! Then flush your eye with water.
Play with contacts or get the "rec specs" from a athletic supply store that they sell for land sports
Ultimately, it depends on what contacts you use and what your optometrist recommends. For most people with soft contacts (hard contacts are now rarely used and offered up), swimming is fine. However, the user should not attempt to open his eyes under the water as the contacts would then easily slip beyond the eye and be forever lost. When in the water, close your eyes when coming into contact with the water (i.e. going underneath the water, swimming across, splashing, etc.) to prevent the contacts from slipping out. When doing vigorous activity in the water (i.e. intense swimming, diving, etc.) where one comes into heavy contact with the water, using goggles would be the safest bet. The pressure of the water could easily push the contacts out.
Silicon Hydrogel(99% water)
It isn't recommended to put your contacts in water. Is it because you don't have any eye-contact solution to leave your contacts in at night? I tried that JUST ONCE overnight and nothing such as irritation occurred but I have heard that if you do leave your contacts in water, a bacteria will form called amoeba and could be extremely fatal and may cause even blindness. Same goes for swimming with contacts in your eyes. Definitely a no, just for your safety :)
If you have water and you've never used it as a resource before then yes it is a alternative resource. eg. if your thinking of building a hydro-electric dam then water is an alternative energy resource to what ever you were using before.
If you do not get the face wet or go underwater, contacts should be fine. If you do get splashed or dunked they are unlikely to be flushed out, but they can hold chemicals present in the pool water against the eye for a longer period than would normally happen if you were not wearing them. Then it would be advisable to take them out! If you wear goggles that would be best!
what should you do when you jump into deep water when wearing a lifejacket
You die a slow and painful death.
Unless you only rarely need glasses, it would be wise to have some sort of contacts. I suggest either night contacts or one-use daily contacts.