On Monday, the can - which was used to moisten the skin of a northern bottlenose whale that became stranded in the Thames and then died - was put up for auction on eBay, with all the profits going to British Divers Marine Life Rescue.
The site said: "Here's your chance to own a symbol of hope, a piece of history and donate to a worthy cause all at the same time."
Bids began at ?5 ($9) but by the end of the day had surpassed ?400 ($715).
As television news channels in Britain reported live from the river rescue and photographs of the operation made the front pages, the watering can featured in many of the shots.
If the buyer wants, the can could be signed by members of the rescue team, including Paul Jepson, the veterinarian who supervised the operation and who on Monday was performing the post-mortem examination on the whale.
Results of the autopsy were expected on Wednesday.
The small, bright red watering can, of the sort usually favoured by gardeners, belongs to Faye Archell, a member of the rescue team.
Made of plastic, Archell has used it during other marine mammal rescues - mostly of porpoises and seals - though this was the first time it had come to the aid of a whale.
It was still not clear what caused
the whale to swim up the Thames
Archell told The Associated Press: "We were splashing the whale, but a watering can is actually much more effective."
The attempted whale rescue was estimated to have cost the all-volunteer charity rescue team about ?5000 ($8800).
The team had co-ordinated efforts to save the mammal.
It was still not clear what caused the six-metre-long whale to swim up the Thames, far away from the northern bottlenose's usual north Atlantic habitat.