EWOT: Comparative Roommates

Lately, I tried to take the idea of two different entities and comparing how they help one another to allow a economic sustainability. Well, in my own room, I started to think about how I sustain both me and my roommate with equal trades. Although it sounds boring, I love water (and liquor) but mostly water. I could drink water over anything and it's hard to live in the Quad without a water fountain nearby to refill a water bottle. So now every three days or so, I buy 3 Liters of water for $2.50. Normally I would drink it on my own but I also feel the need to give some to my roommate since he too would like to quench his thirst. But lately, I've been getting somewhat annoyed that he receives the water for free. So a couple of days ago, I decided that every time I would buy the 3 Liter water bottle and he wanted some to drink, he would have to do two problems of Webwork. Normally it takes about 5 to 10 minutes to finish the problems but if he is capable of doing it, he'll be able to gain access to the water. Since he does not have enough declining left, I think it would be somewhat worth it to do two problems that I have a hard time doing for the access of good quality water in comparison to fountain water, (it tastes like iron) and Wilson Common water, (it's a pain walking back to a cup of water.) Now I have less time to work on the Webwork since I take 15 to 20 minutes to do 2 problems and he has access to water that I bring on my own during the week.