Rain catchment system physics question

In summary, the rain catchment system will work and will have equal water levels in the red pipe and the tank. However, if there is a leak in the system, the tank will eventually fill up and the water will flow down the red pipe and into the ground.
  • #1
Physiogista
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I am volunteering at an orphanage in Guatemala. There is no well, and the city water is a relatively expensive. I would like to install a rain catchment system on our roof for use in the outhouse bathroom and garden. I've diagrammed it and attached the image.

My question is this: Will the water tank completely fill up, or will the water level in the water tank stay at the water level of the red pipe? My education says that the rain will fill up the very bottom of the tank, then the flat part of the red pipe, and then continue to fill the tank and up the red pipe in such a way that the respective water levels are equal. However, common sense seems to be saying that the tank will not fill up past the level of the flat red pipe section because the water has to "push" its way up the tank.

Will this system work? Is my common sense concern reflective of reality?
 

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  • #2
The vertical part of the red pipe would have to have more volume then the tank for this to work. I am no expert, but I would place the red pipe at the top of the tank.
 
  • #3
Physiogista said:
My question is this: Will the water tank completely fill up, or will the water level in the water tank stay at the water level of the red pipe? My education says that the rain will fill up the very bottom of the tank, then the flat part of the red pipe, and then continue to fill the tank and up the red pipe in such a way that the respective water levels are equal.
Yes that is correct. Assuming the top of the tank has a hole somewhere the tank can fill to the level of the red pipe inlet. ie the gutter height.
leaks are twice as likely as a top filled tank and the pipe may be more vulnerable to damage on the ground, A stray spade strike and the tank empties.

Why can't you go overhead? A hose tied to an overhead rope/cable strung between the house and tank works. Depending on catchment size, rain fall, flow rate structure strength, span length etc of course.
 
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Likes Brent White
  • #4
Welcome to PF.
The red pipe and tank here form what is termed an “inverted siphon”.
The top of the tank must have a small air vent.
Place a stop valve at the tank where the red pipe attaches so you can service the red pipe without draining the tank.
The tank only needs one drain/fill hole, the brown pipe can come from a 'T' in the red pipe.
 
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Likes Jeff Rosenbury and Redbelly98
  • #5
Thank you all!
 

1. How does a rain catchment system work?

A rain catchment system works by collecting rainwater through a series of gutters and downspouts that lead to a storage tank or cistern. The water is then filtered and stored for later use.

2. What is the physics behind a rain catchment system?

The physics behind a rain catchment system involves the principles of fluid dynamics. The gutters and downspouts are designed to channel the rainwater into the storage tank, and the tank is designed to withstand the weight and pressure of the collected water.

3. How much rainwater can a rain catchment system collect?

The amount of rainwater a rain catchment system can collect depends on the size of the catchment area and the amount of rainfall. On average, a 1000 square foot catchment area can collect about 600 gallons of water from 1 inch of rain.

4. What are the benefits of using a rain catchment system?

There are several benefits of using a rain catchment system, including reducing water bills, conserving water resources, and providing a backup water supply during droughts or emergencies.

5. Are there any limitations to using a rain catchment system?

One limitation of using a rain catchment system is the initial cost of installation. Additionally, the effectiveness of the system depends on the amount and frequency of rainfall in the area. It may also require regular maintenance, such as cleaning and replacing filters, to ensure the system functions properly.

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