Every Wednesday in the summer we have Water Balloon Wednesday.
Water Balloon Wednesday is a day where I have about 500 water balloons blown up, ready for a HUGE water balloon fight. Then I fill two kiddy pools up with water and give them these cool squirt guns to use. We do this in the front yard so the neighborhood kids can join in.
Last summer I had a small water balloon business where I sold filled water balloons, I always felt guilty for having 1000's of filled balloons and not being able to let the kids use them, so this summer I did not do my business. (My grandmother has dishes of fake cookies and candy sitting out, as a kid it felt like torture, I think what I did last summer was the same) SO! Let them have the balloons! They love them.
To answer a few questions you may or may not have - Yes I am pretty fast I can do about 200 balloons in an hour. I fill them at night while I watch TV with my husband. Its less intense now since its just for my kiddos and not someone expecing an order. I don't really count or time myself anymore. There is no real trick you just become faster and better with the more you tie.
Some balloon info you may not know:
Keep balloons out of direct light (it weakens the rubber)
You can fill balloons a week or so in advance
If you are worried about them busting you can add water to relive pressure on the bottom balloons
Happy Water Balloon Wednesday!