Why even though the global human population's growth rate is declining the human population is growing?

An analogy might be filling a bath - you start of with the taps on full - but as the bath gets close to where you want, you begin to turn the taps down.

The FLOW rate of water from the taps is DECLINING - but the level of the water in the bath is stillINCREASING.

In short the SPEED of increase is going down - but it is still increasing nonethless.

Hope the bath analogy helped.

Mark