RAIN WATER HARVESTING

Suppose u have a house that measures 12m by 12m (i.e 40X40ft), this means that the amount of water u can collect in a year is 12X12X1.2=172.8cc or 172,800liters. (Here, we take the annual rainfall is 1200mm).

According to demand, for a middle class household, the daily demand is 150liters per day per person, which is to say 54,750liters annually. For a house with a dad, mom and 2 kids, the figure is 219,000liters.

This means, if you can be able to collect all rain water, this is 78.9% of your demand.

Size of the tank will be derived from a mass curve (cumulative demand vs cumulative rainfall curve).

To cut my long story short, am strongly advocating for RAINWATER HARVESTING from roofs, rocks, streams etc.

For any details, don't hesitate to consult a water engineer. Here at Kenya, someone needs to come up with a policy that all buildings MUST be fitted with a rainwater collection mechanism and the government gives incentives (tax laxes on construction equipments and fuel) to individuals and corporates that harvest's rain.

how much is a 1000 liter plastic water tank, the cylindrical ones?

Flush toilets are a total waste....Or are there economical ones which uses less than 5 litres per session?

Between 8 and 10k depending on where you are

Yeah there are. I think they use 2litres per flash. A number of institutions are using this nowadays.