The problem as I see it, would be to ensure the water in a 55 gal drum is truly sterile and is that sterility maintainable. Introduction of oxygen (aeration) is of little value until you go to drink the water (strictly for taste).

As to your question, even if the water was sterile to start with, the use an aquarium pump (assuming you can sterilize the internal workings of the pump) to aerate the water would likely result in contamination with airborne organisms.

I would look to long-term storage of water by treating the water with 2-3 times the normal bleach concentration, first ensuring the type of container will not be adversely affected by bleach and that your starting water quality (in term of organics, heavy metals, etc.) is in acceptable ranges. Most food grade 55 gal drums should be fine. I recently purchased two drums, one of each type from this Ebay seller. He has increased the prices quite a lot, since I purchased mine and you may want to check around before purchasing any from him/her. I have not used mine yet, but based upon the description, they are likely the best quality drums on the market.

Blue Light - Water Drums

Pete