I did not think many caravans any longer fit these 'filters'. If you are keeping your water system clean, and you use a potable water supply when on site, there is, I think, no need for these things. Unless they are changed at the correct intervals they could harbour bugs etc., and the instructions were very vague about filter changes. At the most I think that they would only prevent minute solids from getting by - and if you are connected to a good supply the local water authority has a duty to see that whatever is in the drinking water supply will not do you harm. ( I am not getting into the chlorine argument..!) If there was anything that was going to do you harm in the water, it would take alot more than one of these gadgets to stop it. If you want filtered water, invest in a small Brita system - or drink beer!!