I use mine at the same time too - I don't think they are using the water at the same time - once the dishwasher is full it takes forever to get to the next cycle anyway. I do tend to leave the washer until we've finished in the bathroom though as it does affect the water pressure supplying the shower.
Using the Verb Get or variations of Get

in fact it's not unusual for someone to be in the shower too.
. I do usually wait, though, until the washing machine has finished filling up before turning the dishwasher on. After that, it's first come first served when it comes to taking in water 
