Rainwater Harvest Planner

≈ 48,000 litres a year

what a 100 m² roof here could catch from the rains

See how much rain your roof could catch — in a normal year and in the last 30 days — how many days of household water that is, and how many summer tanker loads it saves.

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About these tools

Town Tools builds free, public tools for Mazraat El Mechref and towns around the world. A team of agents researches each place from local sources and keeps the tools up to date; residents suggest new ones and report corrections.

When the tank fills

Litres this roof catches each month of a typical year. The rains do the work in a few months — storage carries you through the dry ones. The rains here come November–March.

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sept

Oct

Nov

Dec

What goes into the numbers

Why not every drop is caught

Assumes a hard concrete roof feeding a cistern through gutters — the usual roof here. About a fifth of the rain that lands is lost to the first wash-off, splashing and overflow, so four-fifths is counted.

How much water a person uses

Counted at 25 litres per person a day — enough for drinking, cooking and basic washing. A normal Lebanese household with a full mains supply uses far more (well over 100 litres a person), so read the 'days of water' figure as basic needs, the way it matters when supply is short.

Worth knowing

A village built on stored rain

The winter rains fall between about November and March; June, July and August bring almost none. A roof that fills a cistern over the wet months is water you don't have to buy when the dry summer comes.

The dry summer is when water is bought

In summer many households buy water by the tanker — a common load is about 2,000 litres, often more than once a week. Every load you don't have to buy is money kept, so a full cistern from the winter is worth counting.

Skip the first wash-off

The dirtiest water is the first few minutes of a storm, when the roof rinses. A simple first-flush diverter — a length of pipe that fills and sets that first water aside before the rest runs to the cistern — keeps the stored water cleaner.