# Question: How Do You Calculate Rainwater Collection On A Roof?

## How much water is in an inch of rain?

Rainfall amount is described as the depth of water reaching the ground, typically in inches or millimeters (25 mm equals one inch).

An inch of rain is exactly that, water that is one inch deep.

One inch of rainfall equals 4.7 gallons of water per square yard or 22,650 gallons of water per acre!.

## How many downpipes do I need for my roof?

From Figure 3.5 (A) in AS/NZS 3500.3, the maximum catchment per downpipe is 47m2. To calculate the minimum number of downpipes, divide the roof catchment area by the allowable maximum catchment per downpipe. To calculate the average catchment per downpipe, divide the roof catchment area by the number of downpipes.

## How do you calculate rainfall on a roof?

To calculate how much rainwater can be harvested, multiply your rainfall (mm) by your roof surface area (m2) being used to catch rainwater. The resulting number represents how many litres of water you can expect to collect.

## How do you calculate rainwater collection?

Simple Rainwater Harvesting Formula – For every 1” of rain and 1,000 square feet of impermeable surface (roof, driveway, etc), about 620 gallons are generated. Meaning, you can capture about . 62 gallons per sq ft. To figure out the square footage of a surface, multiply the width x length.

## What is a simple method of rainwater harvesting?

Barrel harvesting It is the simplest method of rainwater harvesting. There is generally a drain on the rooftop or terrace, to which you connect a strong pipeline. Let this pipeline be connected to a large barrel. You can also have multiple barrels if it is a high rainfall receiving area.

## What does 10mm of rain mean?

10 mm rainfall means that if rainfall fell on a flat land surface , with no slope ,no evaporation, and no percolation of water I.e. water does not go underground, then the amount of rainfall would be 10 mm measured from the ground. Now this is practically not possible ,so ideally rain gauge is used to measure rainfall.

## How do you calculate roof catchment area?

This capacity can be calculated using the following formula: Annual rainfall (in millimetres) x Roof surface area (in square metres) = Roof catchment capacity. This is an important figure to understand so you can design a Rain Harvesting system and choose a tank size that will meet your water volume requirements.

## How do you calculate roof area on plan?

Multiply your house length by your house width to get the area. (For example, 40 feet x 30 feet = 1,200 square feet.) Next, multiply the area by your roof’s pitch. (1,200 x 1.05 = 1,260 square feet.)

## How do you calculate rainwater runoff from a roof?

To calculate how much rainwater can be harvested, multiply your rainfall (mm) by your roof surface area (m2) being used to catch rainwater. The resulting number represents how many litres of water you can expect can collect.

## How much water is collected from a roof?

Approximately 550 gallons of rainwater can be collected for every 1000 square feet of collection surface per inch of rain. To estimate amount collected in one year, take the square footage of your collection surface, divide by 1000, multiply by 550 and then multiply by the average annual rainfall for your area.

## How do I calculate roof drainage?

Take the roof’s total square footage and divide by the total square footage handled by one drain. The result is the number of drains needed. For example: 50,000 / 4,400 = 11.36; or 12 drains required.

## How fast do rain barrels fill up?

How quickly will my Rain Barrel fill up? Pretty darn quick! A half inch of rain collected from just a 200 sq. ft.

## How can rainwater be collected?

Rainwater harvesting is collecting the run-off from a structure or other impervious surface in order to store it for later use. Traditionally, this involves harvesting the rain from a roof. The rain will collect in gutters that channel the water into downspouts and then into some sort of storage vessel.

## How many Litres is 1mm of rain?

A rainfall of 1 mm supplies 0.001 m3, or 1 litre of water to each square metre of the field. Thus 1 ha receives 10 000 litres.