In this chapter, some common techniques are described for the measurement of water levels, drawdowns, and discharges. Any successful application of the methodologies presented in the following chapters depends on the precise and accurate field and laboratory measurements of the medium and flow properties. No doubt, in earth sciences the quantities vary within short distances and the aquifer properties may have as many different values as the number of samples taken in the field. However, because of the extensive flow domain their averages give satisfactory results for practical purposes. On the other hand, some of the parameters need to be measured with more care and accuracy than others. It is, therefore, a prerequisite to know the error limits of the measurements in arriving at meaningful, representative, and valid practical results. Although the sensitivity of any person to obtain precise results makes him collect as many data as possible to reduce the error band, it may not be practical to do so due to the cost of data and limited time available. It is necessary therefore to accept a certain error percentage in the results which should be less than 10%; concerning decision variables for design less than 5% is preferable. For instance, as mentioned earlier it is difficult to find pure steady state in nature. However, a substitute of this state as a quasi-state can be adopted. What would be the difference between two successive groundwater level measurements to accept quasi-steady state? If the two successive hydraulic head measurements in an observation well are hi and https://www.w3.org/1998/Math/MathML"> h i + 1 ( h i > h i + 1 ) https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781315137612/adc3c630-7630-46b2-9896-5bf34cdfa13d/content/eq102.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> then the relative error percent, α, can be evaluated as () https://www.w3.org/1998/Math/MathML"> α = | h i − h i + 1 | h i × 100 https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781315137612/adc3c630-7630-46b2-9896-5bf34cdfa13d/content/eq103.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>