■Is the location "before and after the inflow"? The water sampling points in the river are selected considering not only the water use points but also locations where the main polluted water has sufficiently mixed after inflow and points before the inflow, as well as locations before and after the confluence of tributaries. By comparing the values before and after, it becomes easier to identify where the water quality changes. ■Sampling at 20% of the water depth in the middle of the river? As a principle, sampling is conducted at the river's center, at a depth of about 20% of the water depth from the surface. If polluted water is flowing unevenly or if the river is wide, the right bank and left bank may be treated as separate points, and the samples from each should not be mixed. ■Sampling after a period of clear weather?! The days for river water sampling are chosen when relatively clear weather has continued, ensuring stable water quality. The survey period includes times of low flow and times when water is being utilized. ■Why sample four times a day? For year-round surveys at key points such as reference points, the principle is to conduct sampling and analysis about four times a day, at least once a month. In areas with less variability, such as upstream sections, the frequency can be reduced. In locations with significant daily fluctuations, surveys may involve sampling approximately 13 times every two hours over two days a year. The timing of sampling is determined considering human activities, factory operations, and the time it takes for pollutants to arrive.

■Should water samples be taken at different depths in ponds and lakes? In lakes and ponds, water quality varies significantly between stagnant and circulation periods, so it is advisable to measure during both periods. During the stagnant period, water samples should be taken at different depths, with standard intervals of 5 to 10 meters. ■What should be recorded on-site? It is essential to record the date and time of sampling, flow rate, rainfall conditions, and major pollution sources nearby. Water temperature, color, turbidity, and odor should be measured on-site as a rule. Samples that cannot be analyzed immediately should be preserved according to the method specified in JIS K0102. The analysis method for each item should also be noted in the results. ■The number of tests is determined by multiplication For example, if three locations are tested four times a year for five items each, that results in 60 items for analysis. When wanting to reduce the number of locations or tests, it is helpful to first determine what information is needed, making it easier to identify areas that can be cut. ■If results are to be presented externally If you plan to submit results, check whether the requesting party is registered under the Measurement Law. In addition to water quality testing requests, our company also offers consultations on rental equipment for measuring total nitrogen, total phosphorus, and COD. Please feel free to contact us for more information.