If the water is properly cleaned and treated before swimming, it can be safe to use rain run-off in a pool.
Then rain falls on a roof and if the roof works properly the rain will drain off of the structure.
so rain water runs off the roof
No, take it off your roof. It will pool up water come spring, and might dent your roof.
To help the rain water drain off easier.
rain and acid wash
It is safe do to so depending on how much snow there is. Start off with standing on a ladder and shoveling it off of the roof. Get as far up as you can and then you can slowly ease your way onto the roof.
Providing the roof covers the same surface area in plan view (looking down from above it, i.e. the ground area covered), then the rain landing on it will be the same. In other words, a high pitched roof would have to be bigger to cover the same plan view surface area as a low pitched roof. For a given area covered by a roof, the pitch of the roof won't matter. If the pitch is so steep that the rain flows off it so fast that your gutters can't cope, then you will lose the rain and fail to collect it. What you need to maximise is the ground area covered by roof. This will maximise the rain you can collect.
Guttering is the general term for gutters, the water channels attached to the side of the roof that direct rainwater pouring off the roof into rain spouts (rather than directly off the roof). See http://www.doityourself.com/scat/guttersanddrainage
a rubber or silver bracelet should be safe in a pool just rinse them off after.
If your zoning board has no restrictions as to how far a pool needs to be from a structure then my advice would be place the pool far enough away from anything that a person might jump off of. example, trees ( besides the cleanup in the pool caused by them) patio roof, sheds, house poles. Remembering when i was a kid we had a pool that we could jump off the patio roof into the pool. My brother did this and ended up splitting the metal side of the pool and ended up swimming in the back yard
1 litre.
It would depend on how far the roof was from the pool! If, for example, the 9 foot roof was in the next town, I would say it is rather doubtful.