Unless you are very unlucky ...

Unless you are very unlucky you are unlikely to encounter bromate in the raw water. 

It is generally formed as a by-product of disinfection and advanced oxidation processes. Whilst chlorine gas is free of it hypochlorite can contain significant chlorate and bromate, especially as older stock decays and if you are chlorinating to a high level such as in super and de-chlorination then the bromate level can exceed the 10 ug/l limit. The way to avoid this is to ensure that you use low bromide/bromate hypochlorite. The same applies where electrolytic hypochlorite is used and in this case you need to specify low bromide salt as a feedstock. 

Ozonation is a major cause of bromate in waters with a bromide content and the way to limit production is to control the ozone dose carefully , limit the contact time so close down parallel contact tanks at lower flows and in extreme cases to pH adjust as it is slower at low pH.  

UV peroxide and UV chlorine can also generate bromate and chlorate and so care is needed. I am currently working on a scheme where additional UV is needed on already chlorine 'disinfected' water and in that case I am having to be careful about the selection of the UV reactors to avoid applying too high a UV fluence at low flows and high UV transmissivities as the turndown range of UV systems is limited. The lamp technology also has an effect and low pressure lamps being near monochromatic at 254 nm are less liable to cause bromate than medium pressure which have a wider range of wavelengths.