How much water your roof could catch in a normal year, which months fill a tank, how many days of household water that is — and how much rain has really fallen in the last 30 days.
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From Town Tools. For the current version, visit https://www.towntools.org/techiman-bono-east-region-gh/rainwater-for-the-dry-months
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 April–October.
JanJan: 788 L
FebFeb: 1,800 L
MarMar: 4,400 L
AprApr: 5,200 L
MayMay: 5,300 L
JunJun: 5,000 L
JulJul: 4,600 L
AugAug: 4,700 L
SeptSept: 7,000 L
OctOct: 6,000 L
NovNov: 2,600 L
DecDec: 860 L
And right now
About 153 mm of rain has fallen in the last 30 days — enough for this roof to have caught roughly 6,100 litres.
These are estimates, not a promise
The catch is plain arithmetic from your roof size and average rainfall — real water depends on your roof, gutters, the first wash thrown off a dusty roof, and how big a tank you have to hold it. Treat it as a starting point for sizing a tank, not a guarantee.
Techiman has two rainy seasons a year, and the pipe supply is the weak link: GWCL’s Tano River system can be stopped for days when illegal mining upstream muddies the river, and one report put it at five days in a row without piped water. Rain is the one reserve a house gets for free. It all runs on your phone; nothing you type is saved or sent.
Live rainfall from Open-Meteo (CC BY 4.0) — a weather-model estimate for the area, not a rain gauge on your street. Updated .
Rain off a roof is not drinking water
Rain off a roof is NOT drinking water as it falls. It carries dust, leaves, bird droppings and whatever sits on the roof and in the gutters, so it must be filtered and disinfected (boiled or treated) before anyone drinks it or cooks with it. Always throw away the first rain of each shower, which is the dirtiest. For bathing, laundry, flushing and cleaning it can be used as it is — and those are most of the water a house uses, so that is where nearly all of the benefit is.
Rainfall varies a lot around here
The monthly rainfall is a 30-year average (1991–2020) for a weather-model grid cell at the town, not the reading of a rain gauge — the model gives about 1,200 mm a year, and local and regional sources quote a range up to roughly 1,660 mm, so treat the figures as the cautious end. Rain also changes a lot between one side of town and another, and the two wet seasons (April to July, and September to October) vary from year to year. Use it to size a tank, and expect your own roof to catch more or less.
What goes into the numbers
Why not every drop is caught
The sum counts on 80% of the rain that lands on the roof reaching the tank. The rest is lost in the gutters, in the first dirty wash that should be thrown away, and in overflow once the tank is full. That 80% is for a hard, smooth roof — aluminium or iron sheets, or concrete. A roof of thatch or one with a lot of moss on it catches noticeably less.
How much water a person uses
25 litres per person per day: drinking, cooking, washing and the bare minimum of cleaning, with no extras. This is the WHO’s basic-access level, an international yardstick rather than a figure of ours.
Worth knowing
Fill the tank before November
In this average the dry months run from November to February: November about 65 mm, December about 22 mm, January about 20 mm. Those are also the months when a Tano pollution event hurts most, because there is no rain to fall back on. The aim is a full tank when the rains stop in October, not a very big tank.
The first rain of a shower
The first few minutes of each shower wash off everything that settled on the roof since the last one. A short upright pipe with a cap that fills first, and is emptied by hand, makes the water going into the tank much cleaner and costs very little.
Keep it covered
A stored-water tank needs a tight lid that keeps light out, or algae and mosquitoes arrive quickly. Keep the water you will drink separate from the water for washing from the first day.
Is the town’s water off right now?
This page tells you what you could store. To find out whether the pipe water is off in your part of town today, use the neighbours’ board. Is the Water Off?.