Readworks Org Answer Key A Drops Journey: Understanding the Journey of a Drop of Water

Water is the essence of life, and it exists in different forms and states. Every drop plays a critical role in the ecosystem and the survival of living organisms. Understanding the journey of a drop of water is essential, and it helps us appreciate the value of conservation and proper management of water resources. In this article, we shall explore the different stages of a drop of water's journey, the challenges it faces, and its significance.

Stage 1: Evaporation

The journey of a drop of water begins with evaporation. Without this process, the water cycle would not be complete. Evaporation occurs when water from the surface of oceans, lakes, rivers, and other water bodies is heated by the sun, causing the water molecules to move faster and escape into the atmosphere as water vapor. This process accounts for about 90% of atmospheric water vapor.

Table 1: Water Vapor

| Water Vapor | % |
| --- | --- |
| Atmosphere | 0.001 |
| Evaporation | 90 |
| Transpiration | 10 |

Source: USGS

Stage 2: Condensation

Water vapor in the atmosphere cools and condenses into tiny droplets that form clouds and fog. Clouds are visible accumulations of water droplets that are held together by air currents. They come in different shapes, sizes, and colors depending on their altitude, temperature, and humidity. As the volume of water droplets in the clouds increases, the droplets come together to form raindrops.

Table 2: Clouds

| Cloud Type | Characteristics |
| --- | --- |
| Cumulus | Puffy and white, often seen on sunny days |
| Stratus | Low-hanging, grey, and flat |
| Cirrus | Thin, soft, and wispy |

Source: National Geographic

Stage 3: Precipitation

The next stage in the journey of a drop of water is precipitation. It occurs when the water droplets in the clouds become heavy, and gravity pulls them down to the earth's surface as rain, snow, hail, or sleet. Precipitation provides essential water resources for agriculture, drinking water, hydroelectric power, and other uses.

Table 3: Types of Precipitation

| Precipitation Type | Characteristics |
| --- | --- |
| Rain | Liquid water droplets that fall from clouds |
| Snow | Ice crystals that fall from clouds |
| Hail | Small pellets of ice that form in thunderstorms |
| Sleet | Small, frozen raindrops that bounce upon hitting the ground |


Stage 4: Infiltration

Once precipitation reaches the ground, it can take different paths depending on the type of surface it falls on. Infiltration occurs when the soil absorbs the rainwater, and it seeps into the ground to replenish underground aquifers and recharge the soil moisture. Infiltration rates are higher in sandy soils and lower in clay soils.

Table 4: Infiltration Rates

| Soil Type | Infiltration Rate |
| --- | --- |
| Sandy | 10-20 cm/hour |
| Loamy | 5-10 cm/hour |
| Clay | 1-5 cm/hour |

Source: ScienceDirect

Stage 5: Runoff

Runoff occurs when precipitation falls on impervious surfaces, such as concrete, rooftops, and pavements, and it cannot infiltrate into the ground. It accumulates on the surface and flows into nearby streams, rivers, and lakes. Runoff can carry pollutants, nutrients, and sediment into water bodies, leading to water contamination and eutrophication.

Table 5: Runoff

| Impervious Surface | Runoff Coefficient |
| --- | --- |
| Asphalt | 0.9 |
| Concrete | 0.7 |
| Metal | 0.6 |
| Vegetation | 0.2 |
| Soil | 0.1 |

Source: US EPA

Stage 6: Surface Water

Surface water refers to the bodies of water that we see on the earth's surface, such as rivers, lakes, streams, and oceans. They are essential habitats for aquatic life, and they provide recreation, transportation, and irrigation. Surface water quality is a measure of the degree of pollution and degradation, and it is essential to protect and conserve it for future generations.

Table 6: Surface Water Quality

| Indicator | Acceptable Levels |
| --- | --- |
| pH | 6.5-8.5 |
| Dissolved Oxygen | ≥ 7 mg/L |
| Biochemical Oxygen Demand | ≤ 5 mg/L |
| Total Suspended Solids | ≤ 25 mg/L |
| Nitrate | ≤ 10 mg/L |

Source: EPA

Stage 7: Groundwater

Groundwater is the water that exists beneath the earth's surface, and it provides drinking water for many people and supports irrigation and industrial activities. It is stored in underground aquifers that are replenished by infiltration, and it can take decades or even centuries for groundwater to replenish.

Table 7: Groundwater Contamination

| Contaminant | Source |
| --- | --- |
| Nitrate | Fertilizers and manure |
| Arsenic | Natural deposits and mining |
| Chloride | Road salt and sewage |
| Pesticides | Agriculture and lawn care |

Source: USGS

Stage 8: Water Use

The use of water is essential for human activities, such as agriculture, industry, and domestic needs. However, the growing population and increasing demand for water have put pressure on the available water resources, leading to water scarcity and conflicts. Water conservation and efficient use can help reduce water stress and ensure sustainable water management.

Table 8: Water Use

| Sector | Water Use (% total) |
| --- | --- |
| Agriculture | 71 |
| Industrial | 16 |
| Domestic | 13 |

Source: FAO

Stage 9: Wastewater Treatment

Wastewater refers to the water that has been used and discharged from human activities, such as toilets, sinks, and industrial processes. It contains pollutants, nutrients, and pathogens that can cause water contamination and health risks. Wastewater treatment is the process of removing these contaminants and making the water safe for reuse or discharge into the environment.

Table 9: Wastewater Treatment

| Process | Objective |
| --- | --- |
| Primary Treatment | Remove suspended solids and sedimentation |
| Secondary Treatment | Remove organic matter and nitrogen |
| Tertiary Treatment | Remove remaining pollutants and disinfection |

Source: EPA

Stage 10: Water Management

Water management involves the planning, allocation, and regulation of water resources to ensure sustainable use and protection of the environment. It considers different factors such as water availability, demand, quality, and social and economic needs. It involves collaboration between different stakeholders such as governments, communities, industry, and non-governmental organizations.

Table 10: Water Management Strategies

| Strategy | Goal |
| --- | --- |
| Conservation | Reduce water use and waste |
| Efficiency | Optimize water use by minimizing losses |
| Reuse | Recycle and reuse water for different purposes |
| Desalination | Convert saltwater into freshwater |
| Integrated Management | Coordinate water management across sectors |

Source: World Bank


In conclusion, the journey of a drop of water is a complex process that involves different stages and challenges. It highlights the interconnectedness of the ecosystem and the importance of water conservation and sustainable management. By understanding the journey of a drop of water, we can appreciate the value of water and take action to protect and conserve this vital resource for future generations.