Poorly rabbits

How do you know when a rabbit is not well... I usually base it on if they are drinking too much or eating less, sitting around and hunched up not interested is a major sign...

BUT what if your bun is eating fine, hopping about ok, interested in everything but drinking more than normal...

Bandit has always been the skinnier of the two bunnies because she is not as food orientated as Smokey is...
Smokey wil take a piece of apple and run off to munch, Bandit will stay where she is have a nibble go off and have a look at what i am doing and then go back to eat... she doesnt eat with massive gusto but will have a good chomp...
Now since they have moved into the wendyhouse they have been drinking more and more water... i have to change their bottle at least once every two days or once a day... the weather has been nice and sunny but not hot and it has been raining so i dont think it is the weather doing it... They get a good amount of hay each day and willow balls to nibble on top of thier daily carrot and spring greens and a small handful of pellets (Excel) in the evening...
I have increased the hay they get and decreased the pellets but veg stays the same...
I have no idea whether before they werent drinking enough ( too much dried food maybe?) or they are drinking too much now?

Can anyone tell me how much water their two buns get through (it is not the gigantic water bottle but the next one down) and suggest a suitable weighing machine so i can keep an eye on Bandits weight please?
I dont want to have to take them to the vet again unless they are losing weight to be honest...

They are fine in themselves it is just the amount of water i need to see about...

Thanks!

most vets will let you use the scales there for free but iweigh me with bobx on scales then me with bun in box on scales and take away original weight of me and box. its no ideal but you will see if weight is changing. also with re the drinnking it depends on where they are getting moisture from mine when are free range in garden drinnk from a bowl and have about 2 licks as the juicy leaves and grass give them all their moisture however if its an indoor bun or a rabbit who lives on a pation and has hay and dried they will drink a lot lot more. when i had some bun s who didnt go out stay with me they drank so much water i was filling it up(a rabbit bowl) every 3 hours...then when i let them in the garden it reduced dramatically. if you are worried they could do a kidney test adn diabetes test at vet via blood test.

Thanks! I was wondering because they get much more hay than they used to (all they used to do before was pee on it, but since litter training them they get a willow ball stuffed with hay every day and i have upped the hay and decreased the pellets ( so eating has changed slightly, i should edit my first post)
I do wash the veg before giving it to them (they like it straight out of the fridge) but maybe they werent getting enough hay before and were not drinking enough? Maybe it is the roughage they get now (their poo is much more hay like rather than all dark brown and smells different whcih is good)

A normal water consumption of a Rabbit is 50-100ml/kg/24hrs.
I they are drinking considerably more than this then an underlying health problem should be considered.

The most obvious thing is the 'health' of the water bottle !! ie is it leaking?

Rabbits with a sore mouth from Dental problems ( eg molar spurs ) often drink a lot as they may not be able to eat as much and so fill up on water.

I would weigh them regularly as weight loss combined with polydypsia can indicate a problem with renal function.

As a precaution I would also treat them with a course of Fenbendazole (Panacur/Lapizole) EC can effect the Kidneys
http://www.rabbitwelfare.co.uk/resources/content/info-sheets/ecuniculi.htm
http://www.petvetcare.co.uk/acatalog/Wormer_for_Rabbits.html

Roughly how much do your buns weigh? I have a pair of cheap digital kitchen scales from Argos, they weigh to the exact gram so they are really sensitive to changing bunny weights, and they do up to 3kg - I put a large dish on the scales and then set them to zero before putting the bunny in.

My vet suggests weighing twice a week and 3 weight losses in a row would give cause for concern if there weren't any other concerns prior to that. If I'm honest I don't weigh all of mine twice a week although I do try to with Santa as she is the small poorly one and weight loss is often her first symptom of a snuffles bout.