I was thinking of customers replies to this the other day and what I'd say, there was recently a study in a paper about how much water is used to wash a car by bucket and buy hosepipe, the results where the bucket was at least 50% more. Before I had triggers I'd use around 30 ltrs for a average house, now with triggers I use around 10ltrs. To wash a car was closer to 60ltrs I think, ask her if she showers every day? If yes then she will probably use more than you do just to do that if you use triggers. Also bullpoo her that you have a massive harvest set up at home so every single bit of rain means your ibcs are full so you don't use much out of the tap at all.