Water tank on Lancashire

Just got back from time away in our new Lancashire. It seems to be a lovely van but the fresh water tank seems to empty far too quickly,( I don't wash up any more than I did in our old smaller Vista van)  and as the meter reads in 1/4s you very soon get the empty tank warning when there still seems to be plenty in there. Does anyone know of a way to adjust this warning level?

Could be like ours was, badly soldered joints on the PCB giving duff voltage and water level readings.
We remade the dry joints and soldered the unsoldered to cure

Thanks for the quick replies. The van is only 8 months old and seems to have a Truma EC300(?) control panel. You can turn the alarm off but every time you use the engine it resets, which is sensible in one way. I guess it will be worth mentioning it to the dealers.

Thanks I will try that and see what happens.

Have just tried the filling and emptying. Thanks for the advice. The % seem to be rather different with 18, 23 or 8 litre gaps and on empty still 14 litres left. Unfortunately our drive isn t level so I have to allow some error for that but at least I now know that I need to fill unto "75%" in order to be sure of a couple of days without a beep. Thanks for your help.

Thanks, I tend to keep everything drained and taps open when at home, just doesn't seem to be a good idea to allow water to sit in a tank for a few weeks before I use it! 
I still hate the idea of carrying lots of water when travelling and since we often do just a few nights away getting water levels right just needs practice, We had our Vista for over ten years so I knew that inside out, now we have a new van I need to get used to its little ways.
And just to be unhelpful our drive is side to side uneven!!!!!

Think I am clear on the way ahead now Thanks for the advice.  
Chris

When traveling I usually add about 10 litres when it reaches 25% as I don't like the idea of a full tank of water sloshing about. We only use the water for washing and cleaning teeth and so far haven't been ill.

I put some baby bottle sterilizing fluid in every couple of months.

On level indications, remember that 75% means that the level is between 75% and 100%. Similarly 0% means less than 25%. The levels are messured in discrete 25% jumps. More unhelpful is that the waste tank is either empty or full! It will read 0% until the level reaches full whrn it will say 100%. On the Lancashire that is a float in the tank and the 50% indication is not implemented.  Daft isn't it?

Just back from 4 days away, filled to 75% and it lasted until this morning, which gives me a good idea of how to proceed. Wouldn't it just be so much easier to have a full empty needle.
Thanks for the suggestions and updates
Chris

Our last van (it was also our first) had an analog needle meter which indicated battery charge or water level depending on the switch position.

But as the tank had sensors in the 25% 50% 75% and full  positions it was no better than the digital readout in our current van.

As I always partially fill the tank from a 10 litre container rather than a hose (always leaving enough in the container for a few brews) then  I have a good idea when to stop for more water. Morrison s supermarkets usually have a tap round the side of the filling station.

Fred