The Laplace Transform of a unit step function $${u_a}\left( t \right),$$ defined as
$$\matrix{ {{u_a}\left( t \right) = 0} & {for\,\,\,t < a\,} \cr { = 1} & {for\,\,\,t > a,} \cr } $$ is

$${\left( {s + 1} \right)^{ - 2}}$$ is laplace transform of

Water distribution systems are sized to meet the

The microbial quality of treated piped water supplies is monitored by