Sorry jgnat - I breeze past a lot - time is short :( I actually haven't firmly defined a sensible definition of what 'good' is, having read Sam Harris' Moral Landscape I was introduced to the novel idea that we may be able to scientifically ascertain the value of each situation. The current debate has a long way to run before our great thinkers have bottomed out at least this approach to defining good. As such it isn't (in my mind) the act of giving the water itself that would be poisoned but the reality of why that exchange took place. If the giving of water is motivated by fear of hell surely that poisons the intention rather than if it was motivated soley by a natural impulse to share and aid. Religion poisons (in my mind) not simply by what it does but by why it does it.
When a religion gives with one hand it expects to receive with the other (have a bible study for free - come join our organisation , body, mind and purse forever). Returning to Mother Theresa as a really good example - a good behaviour (care for needy) was poisoned by a religious devotion to anti-social policies (she was anti contraception, anti modern medicine, alledgedly used less than 10% of donations on charity work etc.) and arguably she perpetuated poverty rather than alleviated it because her attitude was poisoned by her faith.
"I think it is very beautiful for the poor to accept their lot, to share it with the passion of Christ. I think the world is being much helped by the suffering of the poor people."