TD5 injectors. Green.

So had the engine management shut down everything a while back, fault no5 injector, had it changed.
Now 2 and 3 are playing up. Going to get them all changed.
Garage advises possible water in fuel may cause issues.
Can any one give us a clue as to why water would cause issues?
Garage said avoid supermarket fuels. However, I see all fuel trucks for regular garages both high street and supermarkets coming in and out of Buncefield, so surely its all the same fuel?

Thanks in advance.

Water can cause corrosion issues inside the injectors. Supermarket fuel is cheaper for good reason. They don't have the same additives and also tend to run their storage tanks down very low. I don't use them unless desperate and even then I only put enough in to get me to a decent fuel station.

I have had my defender TD5 since 2006 and have had new Volvo D5 diesel XC90's from 2008 up to my latest new 2017 XC90 and all have ran perfectly well using nearly exclusively ASDA standard diesel, I have never had any fuel issues or had to drain any water from the fuel filter.
However I will not use Tesco fuel as I have read of many issues with drivers filling up at Tesco and ending up calling the tow truck. Some ending up having to replace the entire fuel system. They have a very poor record.