I was warned about the heat in July/August but figured since I live in a warm climate in the U.S. I'd be fine.
No such luck.
Be aware: air conditioning is not common in Spain. I was fortunate enough to have AC in my room for the seven weeks I lived there, but it did not exist anywhere else in the apartment. The heat combined with the smoke from their cigarettes was dreadful and no amount of cold showers could cool me off. Also, Madrilenos are out in the street DOING things--not holed up in their rooms--so even if you have AC it's good for the siesta only. And most of the fancy restaurants have AC, but the best cheap food is in the cafes, and most of them had very weak AC or none at all.
My tips? 1) If you're out and about and feeling overheated, grab a bottled water and go to the Corte Ingles. It's one of the few air-conditioned places and most of them have a cafe in the basement where you can sit and have tortilla. 2) Eat light--I lost 12 pounds that summer from eating cold Spanish soup (gazpacho) a few times a day and constantly drinking water.
3) If you are friends with Spaniards, remember they are not used to having AC like we are and do not need to "adjust." Don't complain to them b/c they won't get it. Just head someplace cool. 4) Think you're going to need a hoodie or a blazer? Forget it. I brought two with me and they just sat in my closet. I bought all new clothes, mostly things I would never wear here. Sleeveless tanks, cotton skirts and dressed, flat sandals for walking, cotton bras. Make sure everything is 100% cotton. You will only get one wearing out of it before you have to wash it, and it's so much cooler. LEAVE YOUR JEANS AT HOME.
The heat was so bad I have held off returning again, but I did enjoy myself.
We are here in the middle of August and it is fairly hot. It is between 30-35c, so please people use sun tan lotion especially on your children. I have seen too many sunburnt children over the past few days. Please be careful.
If you travel to Madrid during the summer, you should know that it gets very warm, especially in the months of July and August. Also the climate in Madrid is extremelly dry. What should you always keep in mind? Ig you travel during the summer months take light and comfortable clothes, take sunscreen with you, drink planty of fluids such as water or isotonic drinks, protect your eyes with goo sunglasses, and finally if it's possible don't stay in the sun too much during the peak sun hours (in the afternoon).
Use plenty of sunscreen. Skin cancer is a risk after overexposure to the sun. You should also guard against sunstroke by wearing a hat and limiting your time in the sun.
Public rest rooms are usually clean, but seldom do they supply toilet paper. It is best to always carry along paper. Some rest rooms in Spain are of the squat-style.
The heat in the city can be nearly killing in late july/august. The Madrileños themselves leave the city whenever they can and call this period Hell in Madrid, literally. Sleeping at night is only possible if you have aircondition