The simplest and easiest way is to get a big utensil and fill it up with water and heat it on the stove. Remember to cover it up, and it gets hot faster.
Another option that we used when we were living as tenants was an electric rod. It costs between 200 to 500 INR and depending upon the wattage heats up water fast - a bucket gets heated in say 15 minutes if you are using an element of around 2KW. It is cheap and electric - so wont work if you have power cuts. But it saves the trouble of lighting up your gas and placing an utencil above it. The bigger the bucket the more water you can heat. Be careful, if the element gets sorted, you might get a shock or even trip your main supply.
Third option is getting an electric water geaser. It has its own pros and cons. Electric water geasers cost from around 4000 INR and move up. All of them have a plastic body, a heating element, a tank, a thermostat and some electronic stuff. The difference between a cheap one and an expensive one is basically the quality of these things. A cheap one may have a steel tank, whereas an expensive one may have a copper tank, and some even have tanks lined with glass - to prevent damage to the tank due to hard water. The life of an element is minimum 3 months, after which depending on the quality of water that you get, it will get sorted. Once it gets sorted, you will experience an electric shock whenever you try getting water from a geaser which is switched on. Imagine getting a "shocking" shower. The worst that can happen is when the tank leaks, it will sort the thermostat, maybe the electronics and you will again get a "shocking" shower - but this time the water might be either very cold or very hot. The thermostat costs around 300 INR, the element costs around 500 INR, the tank costs around 1000 INR. Other logistical issues with a storage type of water heater is the pressure. In case you are on the ground floor and the water comes from a tank at the 10th floor, the pressure will be too much for the tank to handle (dont worry, it wont explode, it will simply leak). To avoid it, you will need to get a pressure valve.
Another option in the electrical segment is the "non-storage" type of water heater. It has an element and heats water on the fly. It is cheaper, cause it does not have a tank but it has not been very successful mainly because the water does not get very hot - just warm. And, again if the element gets sorted, be ready to experience a "shocking shower".
If we move out of the electrical option, there are two other options available, the solar option and the gas option. Lets talk about the gas option.
No this is not the "heat in pan" option. There are geasers available in market which run on gas and heat water. Basically a gas geaser has two inputs (water & gas) and an output (hot water). It does not store water. Water runs through pipes among a burning stove and heats up. The cost of a gas geaser is around 2500 INR with installation - you need to have your own gas supply ofcourse. Again this thing does not have a storage, so water is heated on the fly. Gas geaser is supposed to be a lot cheaper (running cost) as compared to an electric geaser - mainly because gas is cheaper than electricity and the effeciency of gas is better than electricity while heating. Here it says that yearly savings are around 3500/- INR. The bad thing about the gas geaser is that it burns up oxygen wherever it is installed. So if you install it in a bathroom without any ventilation, you might experience dizziness due to low oxygen. This geaser has to be installed near a open window so that it gets all the air it can burn. Installation and usage in a non-ventilated space may cause Carbon Monoxide (CO) poisoning (if there is not enough oxygen to burn CO is produced). So be careful while using it. The benefit as compared to electric water heater is the cheaper running cost and the possibility of not getting an electric shock.
And the last one is the solar water heater. Unless you are not living in an appartment and have your own private sunlight from morning till night, it is not worth exploring. Solar water heaters are a lot expensive but environment friendly and very safe.