The missionaries tell me of an unusual problem in Central America. It seems in two story houses The bathroom must be on the ground floor. You cannot install a bathroom on the second floor because the municipality has low water pressure. Is there an inline pump that could augment the low water pressure?

Booster pups re available.

https://www.youtube.com/watch?v=VJS4eO4GF40

Hmmm... I think if water has enough pressure to get to your first floor toilet, it will have enough pressure to get to you second floor toilet. To answer your question: yes, there are all kind of "booster" pumps that would increase pressure in your plumbing system.

But first, do a test: hook up a hose to your garden hose valve on the ground floor, turn faucet ON, and raise the hose to the second story. See if you get any water out from the hose.

Milo

They are some great ideas. Thanks

Also, since it rains a lot in So.America, this is what you can do: put a large barrel ( or any kind of large container ) on the roof to collect rain water. Drill a hole on the bottom of the barrel and attach a small hose to it. Lead the hose to the toilet's angle stop ( valve ) and connect it. Rain water will fill the toilet tank by gravity.

Milo

Milo idea are both good , though for the hose test , make sure the hose you use is around the same diameter as the plumbing pipes you are going to use for the Toilet and I am also guessing wash basin upstairs. I would also when doing that test take it 2 meter higher than where you are going to place the Toilet this insuring that you have optimal pressure.

The Rain Water Tank idea is also a good one , though I am wondering how does it get filled .Generally a rain water tank is filled with rain water from a roof.

Just saying if it's like the diagram is suggesting ( Above ) as in an open rain water tank with no roof feed, it would have to be a big open tank to catch enough water to work than a Roof filled rain water tank.

Actually I just re looked over ways I've done it , the tank could be filled with both rain water and buckets of water. If you really want to have a good system you could also equipped a gauge ( A bit like a fuel gauge ) to the system with a light at the end . When it's just about to get empty the light turned on.