Will a fire hydrant in my residential property lower its value?
If you have tried a new battery and are still having the problem, I would replace the detector. Smoke detectors have a limited life of 7-10 years depending on the model. It is easiest to get the same brand/style so it is compatible with the rest of the system.
Obviously, there is a lot of extraneous water at the scene of any fire. So what you see may be spray off from the nozzles, runoff, or water reflecting / spattering away from the building. Although the attack fire hose with threaded connections generally has a special fire hose thread (NST / National Standard Thread) with flattened peaks, and a special starting point, called a Higbee Cut, to insure easy threading together under fire ground conditions, there can be 1) wear on the gaskets, 2) the gaskets can take a compression set, 3) and the coupling can become loose due to vibration or impact. The hose is stored in the bed of the truck folded, with the lengths already coupled together, so that is ready for a quick deployment. If the couplings were leaking any significant amount, the firemen could tighten them at the scene. Standard Municipal Fire Hose is generally Double Jacketed, which means it has two woven polyester jackets covering the THIN inner rubber tube. These Municipal Fire Hoses are generally coated with an anti-abrasion coating (usually YELLOW or RED ), however they can be punctured fairly easily. Imagine what would happen to your skin if you pushed a pin through two layers of socks, as an example. So any punctures that occur, at the fire scene will spout water while the line is pressurized. Leaking hoses would be taken out of service when identified, or at the presssure testing that regularly occurs.
When a smoke detector is removed and the batteries are removed and it keeps chirping it is a sign that it is dying. Time to replace it.