A few weeks ago, I carried some drinking water to an apartment on third floor (counting the floor immediately above the ground floor as the first floor).
I made two trips, carrying 10 litres each trip, and after that I felt started feeling some sweat breaking. I was a little surprised, seeing that I had made just two trips.
So yesterday, I decided to add weights to the stair workout that I sometimes do when I do not feel like going out for a sprint session. I filled two plastic containers with water, each with a capacity of 5 litres (about 1.3 gallons), for this purpose. One litre of water weighs 1 kilo (2.2 pounds), so each container weighed 5kg (11 pounds).