I like these housing units and have two of them, but it can be a bit tricky to re-assemble after replacing the cartidge. I have found that it is essential to completely lubricate the o-ring and the threads, otherwise the seal is poor and there is a lot of leaking after the water is turned back on. I think in our case we have a lot of iron in the water, which adheres to the o-ring and makes it bind when screwing the blue housing back into the top part of the filter. If the o-ring becomes distorted, it does not seal well. The recommended silicone lubricant is expensive and hard to find. I have been using petroleum jelly (less than $2 for a big jar at any drug store) with no issues. For me at least, there was no need to lubricate on first use, as the o-ring was new and clean. But on two subsequent occasions when I tried to replace the filter cartridge and didn't bother to lubricate, I had a very difficult time getting it to re-seal. Lubrication resolves this difficulty completely.
