For example, on a 2,000 square foot roof, you can collect 2,000 x 0.56 = 1,120 gallons/inch of rain. If your average rainfall was 25 inches/year, your annual collection potential is 1,120 x 25= 28,000 gallons/year.

## How do I calculate how much water my roof holds?

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 do you calculate rainwater collection on a roof?

Roughly speaking, 1 millimetre of rain over 1 square metre of roof equals 1 litre of water. This capacity can be calculated using the following formula: Annual rainfall (in millimetres) x Roof surface area (in square metres) = Roof catchment capacity.

## How do you calculate rainwater volume?

Formula: Area (Length x Width) x Rainfall

- A = Length of the roof area.
- B = Width of the roof area.
- C= The amount of rainfall in inches.
- The formula is A x B x C = Water Volume.

## How many gallons run off a roof?

When you look at the numbers, it’s surprising how much water you can collect every time it rains. Just a half inch of rain falling on a 1,000-square-foot roof will yield 300 gallons of water.

## How much water comes off my roof when it rains?

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 my water usage?

Meters record how much water has been used. Deducting the current meter reading from the previous reading will tell you how many units of water you have used since your last meter reading. To determine your dollar amount of water consumption, multiply the units used by your current water rate.

## How much rain does it take to fill a rainwater tank?

An average 4 bedroom house has a roof surface area of approx. 200 square metres. So, if you have an average 3 bedroom house and a 3000L tank, it would take 20mm of rain to fill your tank. On average each of us uses 147 litres of water per day.

## Is 14mm of rain a lot?

Moderate rain: Greater than 0.5 mm per hour, but less than 4.0 mm per hour. Heavy rain: Greater than 4 mm per hour, but less than 8 mm per hour. Very heavy rain: Greater than 8 mm per hour. … Heavy shower: Greater than 10 mm per hour, but less than 50 mm per hour.

## What is MM IN RAIN measure?

The most common rainfall measurement is the total rainfall depth during a given period, expressed in millimeters (mm). For instance, we might want to know how many millimeters of rain fell over the course of 1 h, 1 day, 1 month, or 1 year. You can easily get a rough measurement of rainfall depth at home.

## How much water is 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 do you calculate runoff factor?

For a given surface area such as a roof or yard, multiply the area by the inches of rainfall and divide by 231 to obtain the runoff in gallons. The factor 231 comes from the fact that the volume of 1 gallon equals 231 cubic inches.

## How many Litres is 1mm of rain?

With a rainfall of 1 mm, every square metre receives 1 litre of rain water. 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.

## How fast do rain barrels fill up?

It’s common for about 1/8″ inch of rain to fall each hour during a moderate rainstorm. That means that a 500 square foot roof can fill a properly installed 50-gallon rain barrel in about one hour.

## How much water does a person use a day?

Estimates vary, but, on average, each person uses about 80-100 gallons of water per day, for indoor home uses.

## Are rain barrels worth it?

Many arid or drought-prone regions have restrictions on lawn watering, and a rain barrel system can be an excellent way to get around these rules. If water use is expensive, capturing precipitation to use in the household can also be worthwhile. … Considering this, a 4,000-gallon system might cost $15,000.