Potable water treatment
Potable water treatment

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Potable water treatment

2.12 Summary

The hydrological cycle is a complex process involving evaporation, transpiration, condensation, air circulation, precipitation, infiltration, surface run-off and percolation. Aquifers are an important source of fresh water supplying about one-third of the UK's potable water demand. Most of the world's water is present as saline water in the oceans.

Self-assessment question

What fraction of the total volume of water that circulates in the Earth's hydrological cycle does river water represent?

Answer

i.e. 1.2 millionths of the total available water.

Self-assessment question

What are the components of the hydrological cycle which can modify the volume of groundwater resources?

Answer

The components are: rainfall, evapotranspiration, run-off, abstraction of surface water, infiltration to groundwater storage, inflow and outflow of groundwater between the aquifer and other areas or the sea, and the change in groundwater storage due to abstraction.

Self-assessment question

Which of the following is the best description of evapotranspiration?

A The transfer of water from the oceans, seas and land surface to the air.

B The accelerated process of transfer of moisture to the air at a water-air interface caused by an external heat source.

C The transfer of moisture from soil to the air through roots and leaves of plants.

D Items B and C together.

E The total removal of moisture to the atmosphere from land surfaces.

Answer

Option D is best, but option E is also valid.

Self-assessment question

How do the following affect infiltration?

(a) Dense vegetation.

(b) Steeply sloping land surface.

(c) Cultivated land.

(d) Roads and buildings.

Answer

(a) Dense vegetation reduces the rate of surface run-off and thus increases infiltration. However, the effect will be offset to some extent by interception, whereby a large proportion of the precipitation stays on the leaves of the vegetation and evaporates.

(b) Water runs rapidly off steeply sloping land surfaces so there is little time for significant infiltration to occur.

(c) Cultivated land is in general subject to greater amounts of infiltration, unless the land is sloping, when the effect will be as in (b).

(d) Tarmac, concrete and roofing surfaces are relatively impermeable, so that roads and buildings promote run-off and reduce infiltration.

T210_1

Take your learning further371

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses372.

If you are new to university level study, we offer two introductory routes to our qualifications. Find out Where to take your learning next?373 You could either choose to start with an Access courses374or an open box module, which allows you to count your previous learning towards an Open University qualification.

Not ready for University study then browse over 1000 free courses on OpenLearn375 and sign up to our newsletter376 to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371