Running the water through a Britta probably can't hurt (at the very least, the charcoal-based filter should neutralize any chlorine in the water) but is still probably less than ideal.

CPs really want water containing less than 100 parts per million of dissolved solids. You should be able to get an analysis of your tap water from your water company. If the tap water is too hard, you can buy distilled water from the store, collect rainwater (just make sure it didn't run off the roof or anything, which might defeat the purpose), or get one of them magical reverse osmosis setups. They're expensive, but it makes sense if your water use exceeds more than a couple gallons a week.

On sick Neppies: not pitchering is often a symptom of not enough light. However, when conditions change, plants often stop growing for a little while, so all you may need to do is wait. I'd also check the bulbs you're using. If the light isn't in the right spectrum and temperature, such as a regular lightbulb like you'd use for your living room, its use for the plant is going to be limited.
There's tons of information (and confusion) out there about lumens and light temperature and spectrums and so forth. I avoid most of it by keeping my plants next to windows so they can get as much natural light as possible. I then point compact fluorescent daylight bulbs at them to supplement. Be carefull of non-flourescent grow lights. I tried some once and wound up cooking my poor Utricularia sandersonni. The flourescents are great because they won't shoot your electric bills through the roof and they don't give off much heat, but they have a limited range of effectiveness: about 12".

If your plants aren't right by a window, or if the light coming through the window is negligable, then I'd suggest getting a fixture for fluorescent tubes, and coating facing surfaces with mylar or some other reflective substance. Essentially, I'd suggest setting up a terrarium.

If there are any pitchers left: are you feeding them? CPs are always happier when well fed.

If there aren't pitchers left, you can resort to what growers of boring, non-carnivorous plants do, and fertilize. I've never done this for a Nepenthes, and I understand you need to be careful about fertilizing most CPs, but The Savage Garden has this to say on the subject (p276): "During the warmer months, apply twice monthly. In winter, once a month will suffice. Apply as a foliar feed, or also through the soil if plants are heavily watered at other times with pure water. Use a 50 percent solution of an orchid or epiphytic fertilizer. Avoid Miracid, which can stunt many Nepenthes."

Finally, here's a CP-oriented forum which has been a pretty good resource for me in the past: www.terraforums.com/forums/index.php

Hope all that helps.