Groundwater is water that exists under the Earth's surface and fills all or part of the void spaces in soils and geologic strata. To distinguish it from surface water, which is found in vast bodies such as oceans or lakes or flows overland in streams, it is also referred to as subsurface water.A submersible pressure transmitter is commonly used to measure groundwater levels. These hydrostatic level transmitters have a tiny diameter and are suspended from the well, borehole, deep bore well or monitoring well by their cable.

WHY IS GROUNDWATER IMPORTANT?

A large portion of the world's fresh water resides underground, stored within cracks and pores in the rock that make up the Earth's crust. For household purposes, almost half of the population of the world relies on ground water. Ground water is used for drinking, irrigation, industry, and cattle in many parts of the world. This is especially true in locations with little precipitation, low surface water resources, or high agricultural and population demand. Ground water is also used by some natural systems, such as wetlands and surface waters fed by springs and seeps.

CONDITION OF GROUNDWATER IN DELHI

India is the world's largest groundwater user. It consumes over a quarter of the world's total, or 230 cubic kilometres per year. In rural areas, groundwater from over 30 million access points provides 85% of drinking water and 48% of water requirements in urban areas. The majority of groundwater is utilized for irrigation, accounting for 88% of total groundwater consumption. Around 700 million Indians live in villages that rely on groundwater for their everyday needs.The groundwater level has dropped by 70-80% in states like Delhi, Haryana, Chandigarh, Himachal Pradesh, and Uttarakhand.

According to a report issued by the Central Ground Water Board, Delhi is India's third most exploited state, behind Punjab and Rajasthan (CGWB). Parts of Delhi experience significant water scarcity every summer. The Yamuna provides over 60% of the water supplied by the Delhi Jal Board, with the balance coming from groundwater. The Yamuna River, on the other hand, is an important source of water and is heavily contaminated with toxic garbage. Furthermore, the direct dumping of wastewater and sewage into surrounding water resources has an impact on the supply of water. According to the CGWB, around 57 percent of Delhi's tehsils are overexploited.

The reason for deteriorating water quality is two-fold:

• - The zones that recharge the groundwater level in Delhi have been obstructed by concrete.
• - Groundwater is extracted for residential consumption in satellite towns like Noida, Ghaziabad, and Gurgaon, indicating that extraction exceeds recharge.

The water table in some of Delhi's most remote areas has dropped by more than three metres every year. According to official calculations, Delhi requires 1,100 million litres of water every day, but the Delhi Jal Board can only supply 900 million litres per day. Delhi's groundwater reserves cover the shortfall of 200 million people. Water supplies in Delhi are fast diminishing due to the city's growing population, which has increased reliance on groundwater.

IMPACTS OF DETERIORATING GROUNDWATER LEVEL

1. Depletion of groundwater will require us to pump water from deeper in the Earth. The more groundwater we remove from under the Earth's surface, the deeper we have to descend to get more. We are finding that there is less water available when we remove water from deeper into the Earth. As a result, we'll have to devote even more resources to developing alternate means for reaching further into the earth.

2. Groundwater depletion will cause large bodies of water to become more shallow. A lack of groundwater prevents more water from flowing into lakes, rivers, and seas. This means that as the existing surface water evaporates, less water will enter over time.Everything in that region, including fish and wildlife, will be affected as the water depth decreases.

3. Saltwater contamination is a possibility. Although we pump groundwater rather than obtaining it from lakes and rivers, this does not negate the fact that it is connected to bigger bodies of water. Deep below groundwater frequently mixes with saltwater, which we should avoid drinking. Saltwater contamination occurs when freshwater and saltwater interact. This type of contamination would raise the cost of drinking water for everyone because pumping and filtering would be significantly more expensive.

4. Food supply and people will suffer when major aquifers are exhausted. Theimportance ofwater and food to our economy and well-being is known to everyone, and it cannot be replaced by any other means.

CONCLUSION

In many places of the world, groundwater resources are not well managed. Simple and effective rules and regulations are required for proper groundwater resource management. The regulating regulations could be based on local knowledge and practical experiences, as well as scientific and field data. It is suggested that groundwater management plans be planned in such a way that:

• 1. Groundwater withdrawals will be altered in accordance with future supply and demand forecasts.
• 2. Within the integrated management system of the entire aquifer field, the renewable character of potential aquifers must be addressed along with appropriate aquifer pump rates, well sites, and relative priority of each sub-aquifer unit.
• 3. Water quality, urbanization's effects, intensive agricultural practices, the economics, social impact, and local administration tactics should all be taken into account.