Groundwater monitoring tools compared

1. Water level sensors: Water level sensors, contact type (pressure transducers) and non-contact, are commonly used to monitor changes in groundwater levels over time. They are relatively simple to install and maintain and can provide continuous, real-time data on groundwater levels. However, without interpolation they do not provide information on the movement or direction of groundwater flow, and they may be subject to drift and calibration issues over time.
2. Groundwater sampling devices: Groundwater sampling devices, such as bailers, pumps and through-flow cells are used to collect water samples from wells and boreholes for field- & laboratory analysis. They can provide detailed information on water quality and contaminant concentrations, but the sampling process can be time-consuming and expensive. Additionally, the samples collected may not be representative of the entire groundwater system, and there is a risk of introducing contamination during the sampling process. These samples often give a static view, which makes them easier to interpret but neglects the actual dynamics happening underground. 
3. Real-time optical sensors for groundwater quality sampling: These sensors operate on the principle of optical sensing and can detect different parameters in real-time without the hassle of taking a sample. The possible drawback is that these results are often not accredited due to not being the result of a standard accredited sampling technique, which often requires the pumping of several times the well volume before taking the sample. Biofouling can also be the source of erroneous readings and may lead to additional & regular calibration intervals.
4. Geophysical methods: Geophysical methods, such as electrical resistivity tomography (ERT) and ground-penetrating radar (GPR), use electromagnetic waves to image the subsurface and provide information on groundwater distribution and movement. They are non-invasive and can cover a large area quickly, but they can be expensive and require specialized expertise to interpret the data accurately.
5. Groundwater flux meters: Groundwater flux meters measure the rate at which groundwater is moving through a given area. They can provide detailed information on groundwater flow direction and velocity and are useful for identifying preferential flow paths and assessing remediation efforts. However, they require specialized equipment and expertise to install and maintain, and they can be expensive and time-consuming to deploy. The accuracy of the information they provide on the underground dynamics compared to static data and modelling of dynamics can be of great value to optimize groundwater processes and remediation efforts.

In summary, each groundwater monitoring tool has its own benefits and downsides, and the choice of which tool to use depends on the specific monitoring needs and requirements of the project. By carefully considering the advantages and disadvantages of each tool, groundwater monitoring professionals can select the best tool. Often the best option is a combination of tools to ensure accurate and effective monitoring of this essential resource