I have a large container which I fill with water using a hose from the tap in bathroom, I have a digital thermometer with a cable and probe that I remove from the tank and plonk in the container, was only cheap but is an excellent thermometer. This is it on ebay http/www.ebay.co.uk/itm/280486816259?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
does not need to be exact, i always aim for 4c below my tank it can stimulate alot of species. However when i was newer to the hobby i would run both taps into a large bowl in the and take a temp reading before hooking up the hose or filling buckets
No need to use thermometers - just judge it roughly with your hand. I always make the water going in a bit colder as it stimulates the changes in the seasons and brings fish into breeding mode and they seem to enjoy it! Your heater will soon bring it gradulally back up to the correct range