house breaking

Question
Hi, thank you for being available. We have an 18 month old dog who has been housebroken since he was 3-4 months old.At 8 weeks he would go to the door to be let out to pee. In these last few weeks he has taken to having accidents on the floor and two nights ago he peed on the bed in our spareroom. He is taken out every night before bed to use the bathroom. Last night we took water away from him at 7 p.m. and he peed on the bedroom floor sometime during the night . He doesn't do this every night and may go weeks or months without doing it. He can be left for hours during the day or night if we are out and never have an accident. He only does this when we are home and sleeping. I hope you can help before he ruins our home. He isn't overweight, he's very healthy, very, very intelligent, has an excellent diet. He does drink a lot of water but has no problem holding it during the day or if we are out. We can't leave him out all night as he would cry and he would be bitten by insects. We don't have a basement to put him in and again he would cry all night as he's always with us. He was sleeping on our bed til a few months ago when I put a stop to it and now he sleeps under the bed or on the lazy-boy chair. He is bonded so tightly to both of us equally that if one of us goes out he pines til we return. We really need some help because this can't go on and when you discover a wet rug in the morning it's too late to correct him then. He knows what he's done is wrong and won't go near the wet spot, hanging his head.  

Answer
First thing you should do is collect a urine sample and take it to the vet to be analyzed as he may have a urinary tract infection or urinary crystals that are causing the problem.  And, I would recommend putting him in a crate at night and remove the water dish.