Rainy days are one of the most difficult part of operating a summer swim team as it is hard to know when to cancel practice, so your best bet is to always come to the pool. Sometimes the weather is "OK" for being outside but we are just waiting our 30 minutes for thunder. When this is the case, the kids usually play kick ball, dodge ball or something in the field with the coaches, or they will stay inside and play games. If it starts to thunder and lightening during practice, they move into the clubhouse and we let them make calls to get picked up. If you cannot come back to get them right away, they hang out inside until their ride comes. That being said, if the weather is dangerous etc, of course, keep your children at home. We have never had dangerous weather at a practice, but we don't want to put anyone in harms way.
While we are on the subject of rain, it never fails that we have some type of rain on a swim meet day. Again, we will swim in the rain, or delay the start of the meet until the thunder/lightening pass. We avoid canceling meets at all costs, as it is next to impossible to make up or get the same line up of swimmers or volunteers. Also, our team, as every other team in the league, has a concession stand during the game. Every team in the league relies on concession funds to help their budget and it is a considerable loss of revenue. Not only do we not make money, but we have spent money for that night either for pizza or chick-fil-a and that is money we lose. Other teams have BBQ, hot dogs etc. and they are in the same predicament.
We of course would never keep the meet on stand by if the weather appears to be dangerous, however, we do wait and check radars to determine how long to delay or to cancel. We again want the kids to get as much "meet" time so they can have all of the opportunities to qualify for swim champs.