You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

As a general rule water that is suitable for humans is suitable for pets - but there are some basic considerations to take into account

Most pets are provided with water from human water supplies - and this is safe. However, strongly fluorinated water may not be acceptable to pets (especially cats). Also mineral waters or fizzy waters may not be acceptable. Often cats may drink running water from a tap, but refuse to drink the same water from a still bowl. Both dogs and cats may ignore still clean water in a bowl, but then be seen drinking from toilets, swimming pools or stagnant rainwater pools ! Quite why they do this is not always clear, but presumably something (smell or taste) is putting them off the clean still water, or something is attracting them to the other water. Fortunately, this behaviour does not seem to result in illness, although it should be discouraged.

There are some sources of water that should be avoided :

• Water associated with sewers - because it may contain toxic waste products or infectious diseases such as leptospirosis which is present in water contaminated by rodent urine
• Water contaminated with blue-green algae - because this can cause serious disease in  our pets
• Highly chlorinated or fluorinated water
• Stagnant water 
• Water that could be contaminated with  toxic waste products - near factory outlets, near livestock farms where slurry may be a problem, in rural agricultural areas where crop spraying with insecticides may have taken place. 
• Hard water with high mineral content - particularly in pets prone to develop urinary stones eg cats with lower urinary tract disease. Generally, water containing less than 5000 parts per million of total dissolved solids (TDS) is considered safe, but over 7000 ppm is better avoided
• Salt water in rocky pools or in the sea is likely to cause stomach upsets and vomiting

Finally if a pet starts to drink too much water (called polydipsia) this can be a sign of disease (eg diabetes or Cushings Disease)  and veterinary advice should be taken.

Updated October 2013