The Main Storage Zones of Water
Watch this video from NASA as a introduction on how water is distributed globally.
So, where is our water? We know that 97% is salt water that we cannot use, so where is the rest??? This graphic breaks it down well:
As you can see, of the 2.5% that is fresh, 68.6% of it is unusable in glaciers and ice caps. 30.1% we can get, but have to pump out of, the ground. Less than 1% of our total FRESHWATER is easily retrieved from lakes and rivers. This makes it extremely important to understand that while it looks like it from space, our water supply for human use is not limitless.
Water Cycles
Global Hydrological (Water) Cycle
The global water cycle is probably the one you first heard about in elementary school. It is a closed system, in that the is a full cycle. Water stays in, on, or above the earth. It does not escape and, thus, we never "lose" or "gain" water. Is goes in and out of different phases, but it is always water. This graphic shows the global water cycle well.
Let's go over some of the processes described above:
Evaporation- When standing water is heated by the sun (or any other process), the water molecules will begin to move rapidly and some will break the barrier between the water and the air and enter the atmosphere. This is the primary process by which water enters the atmosphere.
Precipitation- Water in the atmosphere will eventually cool. It can then form liquid droplets in the form of clouds. When there is enough condensation, the droplets will fall to the surface of the Earth.
Interception- This term is not in the above graphic, but interception is when precipitated water does not reach the soil below. This primarily happens with tree leaves and leaf littler. It can reduce the recharge of aquifers of surface waters.
Runoff- When precipitation falls and hits ground, it will "run off" to the lowest elevation. If enough collects, the runoff can form a river and will eventually end in a lake or larger water body (ocean, gulf, sea). Snow melt will also provide runoff.
Infiltration- Any water that is absorbed by the soil will then "infiltrate" or percolate until it collects below the surface. The rate of infiltration is very important to both how quickly groundwater or an aquifer is able to be recharged (quicker rate = faster recharge) AND how well soil is able to absorb water (lower rate = more absorption), which is important for agriculture.
Groundwater- Water that is infiltrated is stored underneath the ground in the aquifer. This is known as groundwater. In Florida, we get our drinking water from an aquifer. In other places, where an aquifer is not available, people get their water from SURFACE water (lakes, rivers, streams, etc.).
The groundwater is recharged over time. If the rate of water leaving the aquifer (via wells being over-pumped for agriculture, drinking, etc.) is greater than the rate of recharge, the aquifer level will drop and may become inaccessible. The water table, shown below, is the point at which the ground is saturated (full to the max) with water. If the water table is higher than sea level, the freshwater will stay; however, if the aquifer is overdrawn, the water table will drop, and if it becomes lower than sea level, saltwater will infiltrate the groundwater, making it unusable. This is called saltwater intrusion.
Also shown in the graphic below are three different types of aquifers that can be used to draw out freshwater. They are:
Evaporation- When standing water is heated by the sun (or any other process), the water molecules will begin to move rapidly and some will break the barrier between the water and the air and enter the atmosphere. This is the primary process by which water enters the atmosphere.
Precipitation- Water in the atmosphere will eventually cool. It can then form liquid droplets in the form of clouds. When there is enough condensation, the droplets will fall to the surface of the Earth.
Interception- This term is not in the above graphic, but interception is when precipitated water does not reach the soil below. This primarily happens with tree leaves and leaf littler. It can reduce the recharge of aquifers of surface waters.
Runoff- When precipitation falls and hits ground, it will "run off" to the lowest elevation. If enough collects, the runoff can form a river and will eventually end in a lake or larger water body (ocean, gulf, sea). Snow melt will also provide runoff.
Infiltration- Any water that is absorbed by the soil will then "infiltrate" or percolate until it collects below the surface. The rate of infiltration is very important to both how quickly groundwater or an aquifer is able to be recharged (quicker rate = faster recharge) AND how well soil is able to absorb water (lower rate = more absorption), which is important for agriculture.
Groundwater- Water that is infiltrated is stored underneath the ground in the aquifer. This is known as groundwater. In Florida, we get our drinking water from an aquifer. In other places, where an aquifer is not available, people get their water from SURFACE water (lakes, rivers, streams, etc.).
The groundwater is recharged over time. If the rate of water leaving the aquifer (via wells being over-pumped for agriculture, drinking, etc.) is greater than the rate of recharge, the aquifer level will drop and may become inaccessible. The water table, shown below, is the point at which the ground is saturated (full to the max) with water. If the water table is higher than sea level, the freshwater will stay; however, if the aquifer is overdrawn, the water table will drop, and if it becomes lower than sea level, saltwater will infiltrate the groundwater, making it unusable. This is called saltwater intrusion.
Also shown in the graphic below are three different types of aquifers that can be used to draw out freshwater. They are:
- Confined- Confined aquifers sit below a impermeable rock/hard clay layer...water cannot escape. They are recharged from a distance. They are usually under immense pressure because of the rock layer, and therefore, if tapped with a well, can produce what's known as an Artesian well. Basically, an Artesian well is a well that does not need a pump...it flows above the water table on its own. They are usually not very susceptible to pollution because of how far away the recharge areas are.
- Unconfined- Unconfined aquifers are close to the surface and are recharged locally by infiltration. They may have an impermeable layer below the aquifer. There's usually not a lot of pressure, since there is no hard layer holding the water in, so when they are tapped for wells, they must use pumping systems. They are more susceptible to pollution due to their proximity to the surface.
- Perched- A perched aquifer is a type of unconfined aquifer that sits above another unconfined aquifer because water infiltrating from the surface is trapped or 'perched' on a shallow impermeable layer. Perched aquifers are important because they are so close to the surface (easy to get to) and they can be the source of natural springs.
Local Hydrological Cycle
While the global hydrological cycle is closed, the local systems (for example Florida) are open. Water gets stored in the ground or on the surface, may increase or decrease the amounts, can move to other regions, etc. This is all based on the climate conditions and how humans use the land. Please read about Florida's water cycle here.
While the global hydrological cycle is closed, the local systems (for example Florida) are open. Water gets stored in the ground or on the surface, may increase or decrease the amounts, can move to other regions, etc. This is all based on the climate conditions and how humans use the land. Please read about Florida's water cycle here.
