Engine running badly

yes water in tank can cause disturbance on the engine even costly damage to the engine! but dont have any effect on the brain(computer) or electric coponents ,if there is water in the fuel then have the tank cleaned ,the hoses blowed trhu,the fuel filter cleaner replace ,if possible the s park plugs replaced ....if the probleme persiste then , is surrely some thing else .it wil be wise to take your vehicle to a repair shop and have it scaned with the bmw apropriete tool and equipement nte that the 2001 bmw is 80% electronic so dnt try to fix it on your own more damage wil occure ......nicolas