Have you understood a certain process? There are two ways to answer this question. The first is: try to explain the process to someone who does not have the knowledge (e.g. your kid or a student); the second one is to model the process by means of a deterministic simulation. Very often these kind of simulations are numerical models with physical and/or chemical parameters and boudary conditions. Using reliable prameters and boundary conditions is the most important part of any modeling work during the calibration of a model, which is nothing else than comparing measured data with the mathematical simulation. Only a sufficiently calibrated and strictly deterministic model should be used for any kind of prognosis regarding the future behaviour of a natural system on earth. **Using a model which contains stochastic (not deterministic) parameters is rather likely coffee cup reading.** Furthermore, all parameters and boundary conditions used are based on experiments, monitored data and/or chemical analyses and contain a certain uncertainty. This uncertainty of the input data will impact the result and has to be documented (via sensitivity analysis). Thus for example the calculated sustainable yield of a groundwater well is not 10.000 m^{3} a day but e.g. 10.000 +/- 1. 200 m^{3} a day.

We can provide help ragarding the following simulations:

- Runoff and river flow, lake and coastal areas
- Saturated and unsaturated water flow
- Geochemical reactions in water (kinetics and thermodynamics)
- Reactive transport in surface water and groundwater