River pollution is a big problem around the world. The pollution in rivers can decrease drinking water quality and the pollution can get into the ground water and this can influence crop growth. 
By placing multiple measurement devices spread out over a river it is possible to quickly see if there is pollution and how this spreads across the river. By mapping the pollution spread in a river, the source of pollution can quickly be determined. If the devices measure pollution, by checking if other devices measured the pollution as well, the flow of the pollution can be determined. By seeing how the pollution spreads the source might also be determined. By having an Internet of Things aspect, the results can be quickly sent to the people that can take care of the pollution, resulting in a quicker response time and knowing quickly where the source of the pollution is located. They can then evaluate what further actions to take.
The device consists of a 5v pro mini atmega328 p 5V which has a very low power consumption when put in sleep mode. When in sleep mode with the power LED removed it draws around 0.054mA. 
The pro mini has a voltage regulator so it can have a varying voltage input. This is useful since a battery does not have a constant voltage output when it is discharged. The pro mini also supplies a constant voltage to the output pins resulting in more accurate measurements.
The turbidity sensor is a gravity analog turbidity sensor. This sensor has a maximal load of 40 mA when in use. The sensor can measure for a prolonged time being constantly submerged in water. The sensor is placed through a hole in the tube. This is waterproofed with the use of an epoxy seal.
There is also a temperature sensor which is waterproof and suitable for constant exposure to water and a longtime usage. The sensors take measurements every 15 minutes. These values get processed by the atmega328. The temperature measurement is also used to make the turbidity sensor measurement more accurate since this measurement can vary due to temperature. 
Sensors such as pH measurement and spectroscopy devices are not added. A pH sensor is not added since most of the sensors are not suited for constant exposure to the outside environment and need to be cleaned regularly. The sensors that can be used for this idea that are suitable are a lot more expensive than the rest of the device. If a device would then be destroyed or stolen it would be rather expensive to replace. A spectroscopy device is not added since they are quite delicate and consume a lot of power and are also quite expensive. By keeping the price per device relatively low it is more accessible around the globe and can be used in more places. If a device gets destroyed or stolen it is way cheaper to replace as well.
This needs to be tested, but a conductivity sensor might be added as well to not only measure the conductivity but to make a rough estimate of the different metal concentrations in the water. The idea is to test the different conductivities of water with different metals dissolved and create a database, which can be used, based on the turbidity of the water, the temperature and conductivity to make an estimate of the different dissolved metals and concentrations. This needs to be tested for reliability before it can be used.
The device itself consists of a waterproof box, in which the electronics are placed making sure they don’t come into contact with water. Through the box there is a tube. This is needed for the sensors since these need to be in contact with the water to take measurements. On both sides of the tube, a metal mesh is attached to prevent big debris to get in the tube and potentially break the sensors. The data gets sent with a LoRa node These can send information over long distances and consume low amount of power making it ideal for IoT.
Because of the simple structure of the device it is easy to manufacture. The device will last for around a year with one battery before it needs to be changed (this needs further testing to be confirmed). The total cost will be around $130 per device. The pro mini can be bought for below $5, the turbidity sensor can be bought for around $10 and the temperature sensor can be bought for around $7. The housing of the device will cost around $20. The LoRa node will cost around $40. There needs to be a receiver for the nodes as well which in some places can be done by a cellphone company for a monthly fee. Or a receiver needs to be placed within a few km range of the node.