Keeping water system bug free

labdog2

What do people do to avoid tummy bugs due to bugs in caravan water systems? We use puriclean at beginning of season to clean aqua rolls and the vans system. After upsets which coincided with caravan trips we used bottled water for drinking and teeth cleaning.
We get through two aqua rolls per day so there is a good flow through and run an aqua roll through when we first arrive on site.   What more can we do ?