Question

Mumbai needs $1.4\times 10^{12}L$ of water annually. Its effective surface area is $600k{m}^2$ and it receives an average rainfall of $2.4m$ annually. If 10% of this rain water is conserved, it will meet approximately

• A. $1\%$ of Mumbai’s water needs
• B. $10\%$ of Mumbai’s water needs
• C. $50\%$ of Mumbai’s water needs
• D. $100\%$ of Mumbai’s water needs

Answer 1

Answer: (B)

Surface area over which rain is received,
$A=600k{m}^2$

$=600\times (10^3{)}^2{m}^2$

$=6\times 10^8{m}^2$

Average rainfall, $h=2.4m$

Volume of water received by rain, $V$

$=A\times h=6\times 10^8\times 2.4m^3$

Water conserved $=10\%$ of volume received by rain

$=6\times 10^8\times \frac{10}{100}\times 2.4m^3$

$=1.44\times 10^8{m}^3$

$=1.4\times 10^8\times 10^{3}L$

$=1.4\times 10^{11}L$

Percentage of total water consumption received by rain is

$=\frac{1.4\times 10^{11}\times 100}{1.4]\times 10^{12}}=10\%$