Yes, try liquid yeast and see if it makes a difference. Make a starter, though. Dry yeast can be a bit hit or miss for me; I've had some give me wild yeast phenolics. More people see to like the Safale dry yeast, so you could try that. See if you can get some GO-FERM and rehydrate your dry yeast before you pitch it; that should help its viability.
Regarding fermentation temps, do you have a cellar? Otherwise you can try the "swamp cooler" approach. Wet t-shirt and a fan. You can also buy a large round plastic laundry tub and put the carboy in there, fill it about 2/3 full of water, and then use frozen 1L bottles of water to keep the temps down. You'll have to swap them twice a day. Dedicated fridge/freezer with a temperature control is always a possibility, but that's $$$.
Sounds like you need to adjust your sanitation regimen too. I agree that water isn't likely your problem. Try yeast and sanitation methods first, along with lower fermentation temps. Then check extract brands/age/condition.