Getting the dimensions right of a UV system for water treatment requires expert know-how
To determine the correct size for a UV treatment system one needs to know the flow-rate and the UV transmittance (UVT) in the water to be treated. When these are known, the UV size can be calculated based on experience and model predictions.
The UVT is a measure to determine how much UV energy you will lose in your fluid 10mm away from your lamp. The more “dirty” your water is, the more energy you will lose and the higher UV capacity you will need to disinfect your fluid. For municipal wastewater, the UVT is normally around 60% (i.e. 40% energy is lost 10mm away from UV lamp) and for RO water UVT is around 98% (only 2% energy is lost).
The UVT can be determined on the spot with a handheld meter. Alternatively, a water sample can be tested in almost all laboratories where the absorbance will be measured on spectrophotometer at 254nm. The absorbance can then be used to calculate the UVT.